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.

ui/src/lib/client.ts

@@ -69,7 +69,7 @@ export interface GatewayClient {
   lobbyCancel(): Promise<void>;
 
   // --- game ---
-  // Stage 13: the play loop exchanges alphabet indices, so submit/evaluate/exchange/
+  // The play loop exchanges alphabet indices, so submit/evaluate/exchange/
   // check-word take the game's variant (to map letters<->indices via the cached alphabet
   // table), and gameState's includeAlphabet asks the server to embed that table.
   gameState(gameId: string, includeAlphabet: boolean): Promise<StateView>;
@@ -82,10 +82,10 @@ export interface GatewayClient {
   evaluate(gameId: string, dir: 'H' | 'V', tiles: PlacedTile[], variant: Variant): Promise<EvalResult>;
   checkWord(gameId: string, word: string, variant: Variant): Promise<WordCheckResult>;
   complaint(gameId: string, word: string, note: string): Promise<void>;
-  /** Hide a finished game from the caller's own lobby list (Stage 17); per-account, irreversible. */
+  /** Hide a finished game from the caller's own lobby list; per-account, irreversible. */
   hideGame(gameId: string): Promise<void>;
 
-  // --- draft (Stage 17) ---
+  // --- draft ---
   /** The player's server-persisted client-side composition (rack order + board tiles), so a
    *  reload or a second device resumes the same arrangement. The JSON is opaque to the
    *  gateway; the client owns the {rack_order, board_tiles} shape. */
@@ -97,7 +97,7 @@ export interface GatewayClient {
   chatList(gameId: string): Promise<ChatMessage[]>;
   nudge(gameId: string): Promise<ChatMessage>;
 
-  // --- friends (Stage 8) ---
+  // --- friends ---
   friendsList(): Promise<AccountRef[]>;
   friendsIncoming(): Promise<AccountRef[]>;
   /** Addressees the caller has already requested (pending or declined); cannot re-request. */
@@ -109,24 +109,24 @@ export interface GatewayClient {
   friendCodeIssue(): Promise<FriendCode>;
   friendCodeRedeem(code: string): Promise<AccountRef>;
 
-  // --- blocks (Stage 8) ---
+  // --- blocks ---
   blocksList(): Promise<AccountRef[]>;
   block(accountId: string): Promise<void>;
   unblock(accountId: string): Promise<void>;
 
-  // --- invitations (Stage 8) ---
+  // --- invitations ---
   invitationsList(): Promise<Invitation[]>;
   invitationCreate(inviteeIds: string[], settings: InvitationSettings): Promise<Invitation>;
   invitationAccept(invitationId: string): Promise<Invitation>;
   invitationDecline(invitationId: string): Promise<Invitation>;
   invitationCancel(invitationId: string): Promise<void>;
 
-  // --- profile / stats / history (Stage 8) ---
+  // --- profile / stats / history ---
   profileUpdate(p: ProfileUpdate): Promise<Profile>;
   statsGet(): Promise<Stats>;
   exportGcg(gameId: string): Promise<GcgExport>;
 
-  // --- account linking & merge (Stage 11) ---
+  // --- account linking & merge ---
   linkEmailRequest(email: string): Promise<void>;
   linkEmailConfirm(email: string, code: string): Promise<LinkResult>;
   linkEmailMerge(email: string, code: string): Promise<LinkResult>;