R6(a): de-stage code, docs, READMEs; split stage6_test

Mechanical, behaviour-preserving removal of Stage N / TODO-N / phase (RN)
references from comments, doc-comments, service READMEs, the current-state docs
(ARCHITECTURE, FUNCTIONAL+_ru, TESTING, UI_DESIGN), config-file comments, and the
.fbs/.proto schema comments. PLAN.md / PRERELEASE.md / CLAUDE.md keep the stage
history.

- Rename the only stage-named identifiers: registerStage8 -> registerSocialOps,
  registerStage11 -> registerLinkOps (gateway transcode).
- Split stage6_test.go: TestEmailLoginFlow -> email_test.go,
  TestGuestAutoMatchLeavesNoStats (+ provisionGuest) -> account_test.go.
- Regenerated proto bindings (push.pb.go, telegram_grpc.pb.go) from the de-staged
  .proto comments; FB Go/TS bindings unchanged (flatc strips schema comments).

go build/vet/gofmt clean across modules; integration typecheck and pnpm check green.

backend/internal/account/account.go

@@ -24,8 +24,8 @@ import (
 
 // Identity kinds recognised by the backend. Email is modelled as an identity
 // alongside platform identities; its confirmed flag is driven by the email
-// confirm-code flow in a later stage. Robot is a synthetic kind: each pooled
-// robot opponent is a durable account bound to one robot identity (Stage 5).
+// confirm-code flow. Robot is a synthetic kind: each pooled
+// robot opponent is a durable account bound to one robot identity.
 const (
 	KindTelegram = "telegram"
 	KindEmail    = "email"
@@ -66,19 +66,19 @@ type Account struct {
 	IsGuest bool
 	// NotificationsInAppOnly confines notifications to the in-app live stream when
 	// true (the default): the platform side-service skips out-of-app push for the
-	// account (Stage 9).
+	// account.
 	NotificationsInAppOnly bool
 	// PaidAccount marks a lifetime one-time-payment account. It is a service field
 	// (no purchase flow yet); an account linking & merge ORs it so a paid status is
-	// never lost when accounts are consolidated (Stage 11).
+	// never lost when accounts are consolidated.
 	PaidAccount bool
 	// MergedInto is the primary account a retired (merged) secondary points at, or
 	// uuid.Nil for a live account. A tombstone keeps the row so the no-cascade
-	// foreign keys of a shared finished game stay valid (Stage 11).
+	// foreign keys of a shared finished game stay valid.
 	MergedInto uuid.UUID
 	// FlaggedHighRateAt is the soft, reversible "suspected high-rate" marker: the
 	// zero time for an unflagged account, otherwise when the gateway-reported
-	// rate-limiter rejections first crossed the sustained threshold (R3). An
+	// rate-limiter rejections first crossed the sustained threshold. An
 	// operator clears it in the admin console; it never gates any request.
 	FlaggedHighRateAt time.Time
 	CreatedAt         time.Time
@@ -430,7 +430,7 @@ func (s *Store) SpendHint(ctx context.Context, id uuid.UUID) (bool, error) {
 // FlagHighRate stamps the soft "suspected high-rate" marker with at, only when
 // the account is not already flagged — the first sustained episode wins, and a
 // re-flag after an operator clear starts a fresh timestamp. An infra marker, not
-// a profile edit, so updated_at is untouched; it never gates any request (R3).
+// a profile edit, so updated_at is untouched; it never gates any request.
 // It reports whether the flag was newly set.
 func (s *Store) FlagHighRate(ctx context.Context, id uuid.UUID, at time.Time) (bool, error) {
 	stmt := table.Accounts.

backend/internal/account/email.go

@@ -33,7 +33,7 @@ var (
 	// ErrInvalidEmail is returned for an unparseable email address.
 	ErrInvalidEmail = errors.New("account: invalid email address")
 	// ErrEmailTaken is returned when the email is already confirmed by another
-	// account; binding it would be a merge, which Stage 11 owns.
+	// account; binding it would be a merge, which the link/merge flow owns.
 	ErrEmailTaken = errors.New("account: email already confirmed by another account")
 	// ErrAlreadyConfirmed is returned when the email is already confirmed by the
 	// requesting account.
@@ -52,8 +52,8 @@ var (
 // Mailer and verifies it, binding a confirmed email identity to the requesting
 // account. Only the SHA-256 hash of a code is stored (never the plaintext),
 // matching the session model. Binding an email already confirmed by a different
-// account is refused (ErrEmailTaken) — merging two accounts is Stage 11 — and
-// using an email as a login is Stage 6, which reuses this mechanism.
+// account is refused (ErrEmailTaken) — merging two accounts is the link/merge flow —
+// and using an email as a login reuses this mechanism.
 type EmailService struct {
 	store  *Store
 	mailer Mailer
@@ -128,7 +128,7 @@ func (s *EmailService) ConfirmCode(ctx context.Context, accountID uuid.UUID, ema
 
 // RequestLoginCode issues a login confirm-code to the account that owns email,
 // provisioning a fresh (unconfirmed) durable account when the email is new. It is
-// the unauthenticated email-login entry point (Stage 6) and, unlike RequestCode,
+// the unauthenticated email-login entry point and, unlike RequestCode,
 // does not refuse an already-confirmed email — that is the ordinary returning-user
 // login. The code is mailed to the address, so only its real owner can complete
 // the login. It returns the target account id for the subsequent LoginWithCode.

backend/internal/account/link.go

@@ -13,14 +13,14 @@ import (
 )
 
 // ErrIdentityTaken is returned when a platform identity being linked already
-// belongs to another account; the caller turns it into a merge (Stage 11).
+// belongs to another account; the caller turns it into a merge.
 var ErrIdentityTaken = errors.New("account: identity already linked to another account")
 
 // RequestLinkCode issues and mails a confirm-code for email to accountID,
 // replacing any prior pending code. Unlike RequestCode it never refuses up front
 // (taken or already-confirmed): possession of the address is the authorization for
 // a later link or merge, and the merge is only revealed once the code is verified,
-// so a probe cannot learn whether an address is registered (Stage 11).
+// so a probe cannot learn whether an address is registered.
 func (s *EmailService) RequestLinkCode(ctx context.Context, accountID uuid.UUID, email string) error {
 	addr, err := normalizeEmail(email)
 	if err != nil {
@@ -94,7 +94,7 @@ func (s *EmailService) verifyPendingCode(ctx context.Context, accountID uuid.UUI
 
 // AccountIDByIdentity returns the account owning (kind, externalID) and true, or
 // (uuid.Nil, false) when the identity is free. It backs the platform-identity link
-// flow (Stage 11).
+// flow.
 func (s *Store) AccountIDByIdentity(ctx context.Context, kind, externalID string) (uuid.UUID, bool, error) {
 	acc, err := s.findByIdentity(ctx, kind, externalID)
 	if errors.Is(err, ErrNotFound) {
@@ -109,7 +109,7 @@ func (s *Store) AccountIDByIdentity(ctx context.Context, kind, externalID string
 // AttachIdentity links a new (kind, externalID) identity to an existing account.
 // A unique-constraint violation means the identity was taken meanwhile, surfaced
 // as ErrIdentityTaken. It is used to attach a platform identity (e.g. Telegram)
-// to the current account during linking (Stage 11).
+// to the current account during linking.
 func (s *Store) AttachIdentity(ctx context.Context, accountID uuid.UUID, kind, externalID string, confirmed bool) error {
 	id, err := uuid.NewV7()
 	if err != nil {
@@ -129,7 +129,7 @@ func (s *Store) AttachIdentity(ctx context.Context, accountID uuid.UUID, kind, e
 }
 
 // ClearGuest removes the is_guest flag from accountID, promoting an ephemeral guest
-// to a durable account once it gains its first identity (Stage 11). It is a no-op
+// to a durable account once it gains its first identity. It is a no-op
 // for an already-durable account.
 func (s *Store) ClearGuest(ctx context.Context, accountID uuid.UUID) error {
 	upd := table.Accounts.UPDATE(table.Accounts.IsGuest, table.Accounts.UpdatedAt).

backend/internal/account/profile.go

@@ -25,16 +25,16 @@ const maxDisplayName = 32
 
 // maxDisplayNameSpecials caps the total special characters (the "." / "_" separators —
 // every name rune that is neither a letter nor a space) an editable display name may
-// carry, so a still-well-formed name cannot be made of mostly punctuation (Stage 17).
+// carry, so a still-well-formed name cannot be made of mostly punctuation.
 const maxDisplayNameSpecials = 5
 
 // maxAwayWindow bounds the daily away window's duration (midnight-wrap aware).
 const maxAwayWindow = 12 * time.Hour
 
-// displayNameRe enforces the editable display-name format (Stage 8): Unicode letters
+// displayNameRe enforces the editable display-name format: Unicode letters
 // joined by single space / "." / "_" separators, where a "." or "_" may be followed
 // by a single space. No leading separator and no two adjacent separators (except
-// "<dot|underscore> <space>"); a single trailing "." is allowed (Stage 17), so
+// "<dot|underscore> <space>"); a single trailing "." is allowed, so
 // "Name_P. Last" and "Anna B." are valid, "Name P._Last" is not.
 var displayNameRe = regexp.MustCompile(`^\p{L}+(?:(?:[._] ?| )\p{L}+)*\.?$`)
 

backend/internal/account/profile_test.go

@@ -12,7 +12,7 @@ import (
 
 // TestUpdateProfileValidation checks that bad fields are rejected before any
 // database access, so a nil-backed Store is enough to exercise the guards. It also
-// confirms UpdateProfile wires the Stage 8 validators (name format, away window,
+// confirms UpdateProfile wires the validators (name format, away window,
 // offset/IANA timezone), not just their unit tests in validate_test.go.
 func TestUpdateProfileValidation(t *testing.T) {
 	s := &Store{}

backend/internal/account/timezone.go

@@ -7,7 +7,7 @@ import (
 )
 
 // offsetZoneRe matches a fixed UTC offset like "+03:00" or "-05:30" — the form the
-// Stage 8 profile editor stores (an offset dropdown rather than an IANA name).
+// profile editor stores (an offset dropdown rather than an IANA name).
 var offsetZoneRe = regexp.MustCompile(`^([+-])(\d{2}):(\d{2})$`)
 
 // parseOffsetZone parses a "±HH:MM" offset into a fixed-offset location, reporting

backend/internal/account/userlist.go

@@ -20,7 +20,7 @@ type UserListItem struct {
 	IsGuest           bool
 	IsRobot           bool
 	// FlaggedHighRateAt is the soft high-rate marker (zero when unflagged), shown
-	// as a badge in the console list (R3).
+	// as a badge in the console list.
 	FlaggedHighRateAt time.Time
 	CreatedAt         time.Time
 }
@@ -105,7 +105,7 @@ type FlaggedAccount struct {
 const flaggedListCap = 200
 
 // ListFlaggedHighRate returns the accounts carrying the high-rate flag, most
-// recently flagged first (R3).
+// recently flagged first.
 func (s *Store) ListFlaggedHighRate(ctx context.Context) ([]FlaggedAccount, error) {
 	rows, err := s.db.QueryContext(ctx,
 		`SELECT account_id, display_name, flagged_high_rate_at