R3: backend rate-limit observability — ratewatch, auto-flag, admin throttled view

- accounts.flagged_high_rate_at baked into the R1 baseline (no prod data; the
  contour schema is wiped after merge); jet regenerated — the regen also picks
  up the previously missing game_drafts/game_hidden models.
- account.Store: FlagHighRate (set-once), ClearHighRateFlag, the flag in
  GetByID/ListUsers and a ListFlaggedHighRate review queue.
- New internal/ratewatch: ingests the gateway rejection reports, keeps a
  bounded in-memory episode window for the console and applies the
  conservative auto-flag (1000 rejected / 10 min, BACKEND_HIGHRATE_FLAG_*).
- POST /api/v1/internal/ratelimit/report (network-trusted, like
  sessions/resolve).
- Admin console: Throttled page (episodes + flagged accounts), a high-rate
  badge in the user list, the marker + operator clear action on the user card.
- Tests: ratewatch unit suite, report-route handler test, renderer cases,
  integration coverage for the store round-trip and the console flow.

backend/internal/adminconsole/templates/pages/user_detail.gohtml

@@ -13,8 +13,14 @@
 <li><b>Paid</b> {{if .PaidAccount}}yes{{else}}no{{end}}</li>
 <li><b>Hint wallet</b> {{.HintBalance}}</li>
 {{if .MergedInto}}<li><b>Merged into</b> {{.MergedInto}}</li>{{end}}
+{{if .FlaggedHighRateAt}}<li><b>High-rate flag</b> <span class="warn">{{.FlaggedHighRateAt}}</span></li>{{end}}
 <li><b>Created</b> {{.CreatedAt}}</li>
 </ul>
+{{if .FlaggedHighRateAt}}
+<form class="form" method="post" action="/_gm/users/{{.ID}}/clear-high-rate-flag">
+<button type="submit">Clear high-rate flag</button>
+</form>
+{{end}}
 </section>
 <section class="panel"><h2>Statistics</h2>
 {{if .HasStats}}