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

pkg/fbs/scrabble.fbs

@@ -321,6 +321,40 @@ table ChatList {
   messages:[ChatMessage];
 }
 
+// --- feedback (authenticated) ---
+
+// FeedbackSubmitRequest submits a feedback message with an optional single
+// attachment. attachment is the raw file bytes (empty for none); attachment_name
+// carries the original file name (its extension keys the allow-list); channel is
+// the submitting platform (telegram/ios/android/web). The response is an Ack.
+table FeedbackSubmitRequest {
+  body:string;
+  attachment:[ubyte];
+  attachment_name:string;
+  channel:string;
+}
+
+// FeedbackReply is the operator's answer shown back to the player.
+table FeedbackReply {
+  body:string;
+  replied_at_unix:long;
+}
+
+// FeedbackState is the player's feedback screen state. blocked_reason is "" (can
+// send), "pending" or "banned"; reply is null when there is none to show. Fetching
+// it (feedback.get) delivers any pending reply, clearing the badge.
+table FeedbackState {
+  can_send:bool;
+  blocked_reason:string;
+  reply:FeedbackReply;
+}
+
+// FeedbackUnread reports whether the player has an undelivered operator reply, for
+// the lobby/Info badge (feedback.unread; no side effect).
+table FeedbackUnread {
+  reply_unread:bool;
+}
+
 // --- account, statistics, friends, blocks, invitations, history ---
 
 // AccountRef is a referenced account with its display name resolved — the shared