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/FeedbackState.go

@@ -0,0 +1,91 @@
+// Code generated by the FlatBuffers compiler. DO NOT EDIT.
+
+package scrabblefb
+
+import (
+	flatbuffers "github.com/google/flatbuffers/go"
+)
+
+type FeedbackState struct {
+	_tab flatbuffers.Table
+}
+
+func GetRootAsFeedbackState(buf []byte, offset flatbuffers.UOffsetT) *FeedbackState {
+	n := flatbuffers.GetUOffsetT(buf[offset:])
+	x := &FeedbackState{}
+	x.Init(buf, n+offset)
+	return x
+}
+
+func FinishFeedbackStateBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.Finish(offset)
+}
+
+func GetSizePrefixedRootAsFeedbackState(buf []byte, offset flatbuffers.UOffsetT) *FeedbackState {
+	n := flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])
+	x := &FeedbackState{}
+	x.Init(buf, n+offset+flatbuffers.SizeUint32)
+	return x
+}
+
+func FinishSizePrefixedFeedbackStateBuffer(builder *flatbuffers.Builder, offset flatbuffers.UOffsetT) {
+	builder.FinishSizePrefixed(offset)
+}
+
+func (rcv *FeedbackState) Init(buf []byte, i flatbuffers.UOffsetT) {
+	rcv._tab.Bytes = buf
+	rcv._tab.Pos = i
+}
+
+func (rcv *FeedbackState) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
+func (rcv *FeedbackState) CanSend() bool {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
+	if o != 0 {
+		return rcv._tab.GetBool(o + rcv._tab.Pos)
+	}
+	return false
+}
+
+func (rcv *FeedbackState) MutateCanSend(n bool) bool {
+	return rcv._tab.MutateBoolSlot(4, n)
+}
+
+func (rcv *FeedbackState) BlockedReason() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
+func (rcv *FeedbackState) Reply(obj *FeedbackReply) *FeedbackReply {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		x := rcv._tab.Indirect(o + rcv._tab.Pos)
+		if obj == nil {
+			obj = new(FeedbackReply)
+		}
+		obj.Init(rcv._tab.Bytes, x)
+		return obj
+	}
+	return nil
+}
+
+func FeedbackStateStart(builder *flatbuffers.Builder) {
+	builder.StartObject(3)
+}
+func FeedbackStateAddCanSend(builder *flatbuffers.Builder, canSend bool) {
+	builder.PrependBoolSlot(0, canSend, false)
+}
+func FeedbackStateAddBlockedReason(builder *flatbuffers.Builder, blockedReason flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(blockedReason), 0)
+}
+func FeedbackStateAddReply(builder *flatbuffers.Builder, reply flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(2, flatbuffers.UOffsetT(reply), 0)
+}
+func FeedbackStateEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
+	return builder.EndObject()
+}