feat(feedback): in-app user feedback with admin review and account roles

User-facing Feedback screen (Settings -> Info, registered accounts only): a
message (<=1024 runes) plus one optional attachment, an anti-spam gate (one
unreviewed message at a time), and the operator's inline reply with a
Settings/Info badge. Server-rendered admin console section (/_gm/feedback):
unread/read/archived queue with per-user search, detail with read/reply/
archive/delete/delete-all, safe attachment serving (nosniff, images inline via
<img>, others download-only). Introduces account_roles, the first per-account
role table; feedback_banned blocks only feedback submission, granted/revoked
from /users and the delete-with-block action.

- migration 00004_feedback (feedback_messages + account_roles) + jetgen
- backend internal/feedback (store+service), internal/account/roles.go
- wire: FlatBuffers feedback.submit/get/unread; gateway guest gate (Op.NonGuest,
  is_guest via session resolve) -> guest_forbidden before any backend call
- reply push reuses NotificationEvent with a new admin_reply sub-kind
- UI: /feedback route + screen, attachment picker, badge, channel detection, i18n
- tests: feedback unit (Go+UI), gateway guest-gate, inttest lifecycle, e2e
- docs: PLAN stage 19, ARCHITECTURE s15, FUNCTIONAL(+ru), TESTING, READMEs

ui/src/screens/About.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
   import { t } from '../lib/i18n/index.svelte';
   import { app } from '../lib/app.svelte';
+  import { navigate } from '../lib/router.svelte';
   import { aboutContent } from '../lib/aboutContent';
 
   // The auto-match move clock (mirrors backend game.DefaultTurnTimeout = 24h).
@@ -31,6 +32,10 @@
   </section>
 
   <p class="muted">{t('about.version', { v: version })}</p>
+
+  {#if !(app.profile?.isGuest ?? true)}
+    <button class="btn feedback" onclick={() => navigate('/feedback')}>{t('feedback.title')}</button>
+  {/if}
 </div>
 
 <style>