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.

loadtest/README.md

@@ -1,6 +1,6 @@
-# loadtest — R2 stress harness
+# loadtest — stress harness
 
-Reusable load harness for the pre-release stress pass (`PRERELEASE.md` R2/R7). It
+Reusable load harness for the pre-release stress pass. It
 seeds a large account population with pre-created sessions, drives virtual players
 through the **gateway edge protocol** in realistic games, hammers the rate limiter,
 and prints a trip-report summary. It stays in the repo for repeats.
@@ -91,4 +91,4 @@ runs unconditionally.
 
 The harness shares the host CPU with the contour, so the early-pass resource baseline
 is read with the harness's own container series in mind; a cleaner number on separate
-hardware is an R7 goal. The moderate ramp keeps the generator from being the bottleneck.
+hardware is future work. The moderate ramp keeps the generator from being the bottleneck.