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/scrabblefb/FeedbackReply.go

@@ -0,0 +1,75 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package scrabblefb
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type FeedbackReply struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsFeedbackReply(buf []byte, offset flatbuffers.UOffsetT) *FeedbackReply {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &FeedbackReply{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishFeedbackReplyBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsFeedbackReply(buf []byte, offset flatbuffers.UOffsetT) *FeedbackReply {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &FeedbackReply{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedFeedbackReplyBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *FeedbackReply) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *FeedbackReply) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *FeedbackReply) Body() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *FeedbackReply) RepliedAtUnix() int64 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.GetInt64(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *FeedbackReply) MutateRepliedAtUnix(n int64) bool {
+	return rcv._tab.MutateInt64Slot(6, n)
+}
+
+func FeedbackReplyStart(builder *flatbuffers.Builder) {
+	builder.StartObject(2)
+}
+func FeedbackReplyAddBody(builder *flatbuffers.Builder, body flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(body), 0)
+}
+func FeedbackReplyAddRepliedAtUnix(builder *flatbuffers.Builder, repliedAtUnix int64) {
+	builder.PrependInt64Slot(1, repliedAtUnix, 0)
+}
+func FeedbackReplyEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}