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

gateway/internal/transcode/encode.go

@@ -324,6 +324,37 @@ func encodeChatList(r backendclient.ChatListResp) []byte {
 	return b.FinishedBytes()
 }
 
+// encodeFeedbackState builds a FeedbackState payload, nesting the reply when present.
+func encodeFeedbackState(st backendclient.FeedbackStateResp) []byte {
+	b := flatbuffers.NewBuilder(128)
+	var reply flatbuffers.UOffsetT
+	if st.Reply != nil {
+		body := b.CreateString(st.Reply.Body)
+		fb.FeedbackReplyStart(b)
+		fb.FeedbackReplyAddBody(b, body)
+		fb.FeedbackReplyAddRepliedAtUnix(b, st.Reply.RepliedAtUnix)
+		reply = fb.FeedbackReplyEnd(b)
+	}
+	reason := b.CreateString(st.BlockedReason)
+	fb.FeedbackStateStart(b)
+	fb.FeedbackStateAddCanSend(b, st.CanSend)
+	fb.FeedbackStateAddBlockedReason(b, reason)
+	if st.Reply != nil {
+		fb.FeedbackStateAddReply(b, reply)
+	}
+	b.Finish(fb.FeedbackStateEnd(b))
+	return b.FinishedBytes()
+}
+
+// encodeFeedbackUnread builds a FeedbackUnread payload.
+func encodeFeedbackUnread(u backendclient.FeedbackUnreadResp) []byte {
+	b := flatbuffers.NewBuilder(16)
+	fb.FeedbackUnreadStart(b)
+	fb.FeedbackUnreadAddReplyUnread(b, u.ReplyUnread)
+	b.Finish(fb.FeedbackUnreadEnd(b))
+	return b.FinishedBytes()
+}
+
 // buildGameView builds a GameView table and returns its offset.
 func buildGameView(b *flatbuffers.Builder, g backendclient.GameResp) flatbuffers.UOffsetT {
 	return wire.BuildGameView(b, toWireGame(g))