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/lib/gateway.ts

@@ -22,8 +22,13 @@ if (isMock && typeof window !== 'undefined') {
   };
   // Drive the auto-match opponent join deterministically from the e2e (the mock otherwise
   // attaches a robot on a timer).
-  (window as unknown as { __mock?: { joinOpponent(): void; joinOpponentSilently(): void } }).__mock = {
+  (
+    window as unknown as {
+      __mock?: { joinOpponent(): void; joinOpponentSilently(): void; adminReply(): void };
+    }
+  ).__mock = {
     joinOpponent: () => (gateway as MockGateway).joinPendingOpponent(),
     joinOpponentSilently: () => (gateway as MockGateway).joinPendingOpponentSilently(),
+    adminReply: () => (gateway as MockGateway).mockAdminReply(),
   };
 }