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/social/adminchat.go

@@ -10,7 +10,7 @@ import (
 	"scrabble/backend/internal/account"
 )
 
-// AdminMessage is one chat message in the admin moderation list (Stage 17): the message
+// AdminMessage is one chat message in the admin moderation list: the message
 // plus its sender's resolved display name and source, for the operator console.
 type AdminMessage struct {
 	ID         uuid.UUID

backend/internal/social/chat.go

@@ -58,7 +58,7 @@ func (svc *Service) PostMessage(ctx context.Context, gameID, senderID uuid.UUID,
 		return Message{}, ErrNotParticipant
 	}
 	// Chat is allowed only on the sender's own turn in an active game; the opponent's-turn
-	// control is the nudge (Stage 17).
+	// control is the nudge.
 	if status != statusActive {
 		return Message{}, ErrGameNotActive
 	}
@@ -115,7 +115,7 @@ func (svc *Service) Nudge(ctx context.Context, gameID, senderID uuid.UUID) (Mess
 	}
 	if ok && svc.now().Sub(last) < nudgeInterval {
 		// The cooldown resets once the sender has acted (moved or chatted) since the last
-		// nudge — engagement clears the "don't spam" limit (Stage 17).
+		// nudge — engagement clears the "don't spam" limit.
 		acted, err := svc.actedSince(ctx, gameID, senderID, last)
 		if err != nil {
 			return Message{}, err
@@ -132,7 +132,7 @@ func (svc *Service) Nudge(ctx context.Context, gameID, senderID uuid.UUID) (Mess
 	if toMove >= 0 && toMove < len(seats) {
 		nudge := notify.Nudge(seats[toMove], gameID, senderID)
 		if lang, err := svc.games.GameLanguage(ctx, gameID); err == nil {
-			nudge.Language = lang // route by the game's bot, not the recipient's last-login one (Stage 17)
+			nudge.Language = lang // route by the game's bot, not the recipient's last-login one
 		}
 		svc.pub.Publish(nudge)
 	}
@@ -140,7 +140,7 @@ func (svc *Service) Nudge(ctx context.Context, gameID, senderID uuid.UUID) (Mess
 }
 
 // actedSince reports whether senderID made a move or posted a chat message in the game
-// after t — the events that reset the nudge cooldown (Stage 17).
+// after t — the events that reset the nudge cooldown.
 func (svc *Service) actedSince(ctx context.Context, gameID, senderID uuid.UUID, t time.Time) (bool, error) {
 	if mv, ok, err := svc.games.LastMoveAt(ctx, gameID, senderID); err != nil {
 		return false, err
@@ -291,7 +291,7 @@ func (s *Store) lastNudgeAt(ctx context.Context, gameID, senderID uuid.UUID) (ti
 
 // lastMessageAt returns the time of senderID's most recent non-nudge chat message in
 // gameID, if any. The nudge cooldown resets when the player chats (or moves), so a stale
-// nudge no longer blocks a new one (Stage 17).
+// nudge no longer blocks a new one.
 func (s *Store) lastMessageAt(ctx context.Context, gameID, senderID uuid.UUID) (time.Time, bool, error) {
 	stmt := postgres.SELECT(table.ChatMessages.CreatedAt).
 		FROM(table.ChatMessages).

backend/internal/social/friends.go

@@ -31,7 +31,7 @@ const friendRequestTTL = 30 * 24 * time.Hour
 
 // accountRef resolves accountID into a notify.AccountRef (the display name from the account
 // store, empty on a lookup failure), for enriching the friend_* live events so the client
-// updates its requests/friends state without a refetch (R4).
+// updates its requests/friends state without a refetch.
 func (svc *Service) accountRef(ctx context.Context, accountID uuid.UUID) notify.AccountRef {
 	ref := notify.AccountRef{AccountID: accountID.String()}
 	if acc, err := svc.accounts.GetByID(ctx, accountID); err == nil {

backend/internal/social/social.go

@@ -32,7 +32,7 @@ type GameReader interface {
 	// has moved); the nudge cooldown resets once the player has taken a turn.
 	LastMoveAt(ctx context.Context, gameID, accountID uuid.UUID) (time.Time, bool, error)
 	// GameLanguage is the game's language tag ("en"/"ru"), so a nudge's out-of-app push routes
-	// to the game's bot rather than the recipient's last-login bot (Stage 17).
+	// to the game's bot rather than the recipient's last-login bot.
 	GameLanguage(ctx context.Context, gameID uuid.UUID) (string, error)
 }
 
@@ -75,7 +75,7 @@ var (
 	ErrGameNotActive = errors.New("social: game is not active")
 	// ErrChatNotYourTurn is returned when a chat message is sent while it is not the
 	// sender's turn — chat is allowed only on your own turn (the opponent's-turn control
-	// is the nudge, Stage 17).
+	// is the nudge).
 	ErrChatNotYourTurn = errors.New("social: cannot chat while it is not your turn")
 )