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.

deploy/caddy/Caddyfile

@@ -2,11 +2,11 @@
 # every operator surface under /_gm (the backend-rendered admin console and the
 # Grafana subpath); the game SPA (/app/, /telegram/) and the Connect edge go to
 # the gateway; the catch-all — notably the public landing at / — goes to the
-# static landing container (R3), so stray traffic never reaches the Go edge.
+# static landing container, so stray traffic never reaches the Go edge.
 # Mirrors ../galaxy-game's /_gm model.
 #
 # CADDY_SITE_ADDRESS is ":80" in the test contour (the host caddy terminates TLS
-# and forwards); set it to a domain in prod (Stage 18) so this caddy does its own
+# and forwards); set it to a domain in prod so this caddy does its own
 # ACME and the contour is self-contained.
 {
 	admin off
@@ -14,7 +14,7 @@
 	# (chat moderation + per-IP rate limiting in the gateway). Test contour: the host caddy
 	# (a private IP) is trusted, so its forwarded client IP is preserved. Prod (no host caddy):
 	# clients connect from public IPs, which are NOT trusted, so Caddy uses the real peer —
-	# the same config is correct (and spoof-safe) in both contours (Stage 17).
+	# the same config is correct (and spoof-safe) in both contours.
 	servers {
 		trusted_proxies static private_ranges
 	}