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/app.svelte.ts

@@ -36,7 +36,7 @@ export interface Toast {
 
 export const app = $state<{
   ready: boolean;
-  /** Whether the live-event stream is connected; drives the matchmaking poll fallback (R4). */
+  /** Whether the live-event stream is connected; drives the matchmaking poll fallback. */
   streamAlive: boolean;
   session: Session | null;
   profile: Profile | null;
@@ -154,12 +154,12 @@ function openStream(): void {
         showToast(t('game.yourTurn'), 'info');
       } else if (e.kind === 'match_found') {
         // Seed the cache from the event's initial state so the game renders instantly on arrival,
-        // then navigate (R4).
+        // then navigate.
         if (e.state) setCachedGame(e.state.game.id, e.state, []);
         navigate(`/game/${e.gameId}`);
       } else if (e.kind === 'notify') {
         // A started invited game seeds its cache so opening it is instant; the lobby badge stays
-        // on the authoritative refresh (R4).
+        // on the authoritative refresh.
         if (e.sub === 'game_started' && e.state) setCachedGame(e.state.game.id, e.state, []);
         void refreshNotifications();
       }
@@ -231,7 +231,7 @@ async function adoptSession(s: Session): Promise<void> {
 }
 
 /**
- * applyLinkResult applies a completed account link or merge (Stage 11): it adopts a
+ * applyLinkResult applies a completed account link or merge: it adopts a
  * switched session (a guest initiator whose durable counterpart won, so the active
  * account changed) or, otherwise, refreshes the current profile in place.
  */
@@ -261,7 +261,7 @@ function syncTelegramChrome(): void {
  * syncTelegramSafeArea mirrors Telegram's content-safe-area top inset (the height its native
  * nav overlays the viewport in fullscreen) into the --tg-content-top CSS var and toggles a
  * `tg-fullscreen` class, so the header can drop below the nav and lift the menu into its
- * band (Stage 17). Called on launch and on Telegram's safe-area / fullscreen change events.
+ * band. Called on launch and on Telegram's safe-area / fullscreen change events.
  */
 function syncTelegramSafeArea(): void {
   if (typeof document === 'undefined') return;
@@ -275,7 +275,7 @@ function syncTelegramSafeArea(): void {
  * syncViewportHeight mirrors the visual-viewport height into the --vvh CSS var so a screen can
  * fit the visible area above an open soft keyboard (iOS does not shrink dvh for the keyboard).
  * On a screen whose input sits at the bottom (chat, word-check) this keeps the input visible
- * without the page scrolling, so the layout no longer jumps when the keyboard appears (Stage 17).
+ * without the page scrolling, so the layout no longer jumps when the keyboard appears.
  */
 function syncViewportHeight(): void {
   if (typeof document === 'undefined') return;