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/model.ts

@@ -105,6 +105,23 @@ export interface ChatMessage {
   createdAtUnix: number;
 }
 
+/** FeedbackReply is the operator's answer shown on the feedback screen. */
+export interface FeedbackReply {
+  body: string;
+  repliedAtUnix: number;
+}
+
+/**
+ * FeedbackState is the feedback screen state. blockedReason is "" (can send),
+ * "pending" (a previous message is still under review) or "banned"; reply is the
+ * operator's answer to show, or null.
+ */
+export interface FeedbackState {
+  canSend: boolean;
+  blockedReason: string;
+  reply: FeedbackReply | null;
+}
+
 export interface Profile {
   userId: string;
   displayName: string;