R3: dashboards, docs and tracker bake-back

- Edge/UX dashboard: aggregate request-rate vs rejection-rate panel
  (gateway_rate_limited_total by class; no per-user labels).
- ARCHITECTURE §2/§11/§12/§13: body cap + explicit h2c sizing, the rate-limit
  observability pipeline and auto-flag policy, the admin-limiter note (and the
  caddy-path gap), the landing container topology; fixed the stale 120/min
  per-user figure.
- FUNCTIONAL (+_ru): the Throttled view and the reversible high-rate flag.
- gateway/backend/deploy READMEs, TESTING.md, root CLAUDE.md updated.
- PRERELEASE.md: R3 interview decisions + implementation refinements logged;
  tracker R3 -> done (this PR implements it; CI gates the merge).

docs/TESTING.md

@@ -76,7 +76,14 @@ tests or touching CI.
   unsubscribe), the transcode round-trips (FlatBuffers↔JSON, X-User-ID
   forwarding, nested GameView, domain-code surfacing), the admin Basic-Auth
   reverse proxy (401 / forward), and a full Connect `Execute` path end to end
-  (guest auth, unauthenticated rejection, unknown message type). The backend gains
+  (guest auth, unauthenticated rejection, unknown message type). **R3** adds the
+  edge-hardening cases: an oversized `Execute` payload is refused
+  (`resource_exhausted`, the `GATEWAY_MAX_BODY_BYTES` cap), a limiter rejection
+  lands in `gateway_rate_limited_total{class}` and the rejection tracker
+  (drain/aggregate unit tests), the report POST reaches
+  `/api/v1/internal/ratelimit/report` with the agreed JSON shape, the `/_gm`
+  mount is 429-guarded by the per-IP admin class, and the gateway's `/`
+  308-redirects to `/app/` (the landing left the embed). The backend gains
   the **guest** lifecycle (a guest plays an auto-match to a natural end yet accrues
   no statistics) and the **email-as-login** flow (request/verify, returning user)
   in `inttest`. Stage 8 adds gateway transcode round-trips for the new social/account
@@ -92,7 +99,12 @@ tests or touching CI.
   404 when not). Postgres-backed `inttest` drives the **complaint resolution →
   dictionary-change pipeline** (file → resolve with a disposition → pending change → mark
   applied), the admin **list/count** read queries, and the **/_gm console over HTTP**
-  (pages render; a resolve POST needs a same-origin header).
+  (pages render; a resolve POST needs a same-origin header). **R3** adds `ratewatch`
+  unit tests (window accumulation, the auto-flag threshold + expiry, the bounded
+  episode map), the account-store **high-rate flag round-trip** (set-once / clear /
+  re-flag) and a console flow in `inttest`: a gateway report auto-flags the account,
+  the **Throttled** page shows the episode and the flagged queue, the user card
+  carries the marker and the CSRF-guarded **Clear** reverses it.
 - **Observability & performance** *(Stage 12)* — `pkg/telemetry` unit-tests the exporter
   selection (`none`/`stdout`/`otlp` build providers; OTLP constructs with no collector;
   the nil-runtime fallback). The domain metrics are exercised through a manual