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/channel.ts

@@ -0,0 +1,30 @@
+// The submitting platform ("channel") reported with a feedback message. Detected
+// from the runtime environment: Telegram Mini App, the Capacitor native shell
+// (iOS/Android), or a plain web browser. No new dependency — the Capacitor runtime
+// global is feature-detected.
+
+import { insideTelegram } from './telegram';
+
+export type Channel = 'telegram' | 'ios' | 'android' | 'web';
+
+/**
+ * detectChannel picks the channel from the runtime signals: telegram wins, then a
+ * native Capacitor platform (ios/android), else web. Pure, so it is unit-tested
+ * without a DOM.
+ */
+export function detectChannel(signals: { telegram: boolean; capacitorPlatform?: string }): Channel {
+  if (signals.telegram) return 'telegram';
+  if (signals.capacitorPlatform === 'ios' || signals.capacitorPlatform === 'android') {
+    return signals.capacitorPlatform;
+  }
+  return 'web';
+}
+
+/** clientChannel returns the submitting platform from the current runtime. */
+export function clientChannel(): Channel {
+  const capacitorPlatform =
+    typeof window === 'undefined'
+      ? undefined
+      : (window as unknown as { Capacitor?: { getPlatform?: () => string } }).Capacitor?.getPlatform?.();
+  return detectChannel({ telegram: insideTelegram(), capacitorPlatform });
+}