Stage 7 (wip): docs bake + stage renumber (insert UI Stage 8, shift +1)

- PLAN.md: new Stage 8 (UI social/account/history); Telegram->9, Admin->10, Linking->11, Polish->12; tracker + Stage 7 refinements; split the Stage 6 'wired in Stage 7' note between 7 and 8
- ARCHITECTURE: promote ui to current (slice scope, board-replay, codegen, theming, mock)
- FUNCTIONAL(+ru): client-app section with the Stage 7/8 split
- README + ui/README + CLAUDE.md: UI build/run/test, codegen, pnpm notes
- bumped Stage 8-11 refs (+1) across docs and code comments

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 10 owns.
+	// account; binding it would be a merge, which Stage 11 owns.
 	ErrEmailTaken = errors.New("account: email already confirmed by another account")
 	// ErrAlreadyConfirmed is returned when the email is already confirmed by the
 	// requesting account.
@@ -52,7 +52,7 @@ 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 10 — and
+// account is refused (ErrEmailTaken) — merging two accounts is Stage 11 — and
 // using an email as a login is Stage 6, which reuses this mechanism.
 type EmailService struct {
 	store  *Store