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

backend/internal/adminconsole/templates/pages/user_detail.gohtml

@@ -1,7 +1,7 @@
 {{define "content" -}}
 {{with .Data}}
 <h1>{{.DisplayName}}</h1>
-<nav class="subnav"><a href="/_gm/users">&laquo; users</a> · <a href="/_gm/messages?user={{.ID}}">messages</a></nav>
+<nav class="subnav"><a href="/_gm/users">&laquo; users</a> · <a href="/_gm/messages?user={{.ID}}">messages</a> · <a href="/_gm/feedback?user={{.ID}}">feedback</a></nav>
 <div class="cards">
 <section class="panel"><h2>Account</h2>
 <ul class="kv">
@@ -67,6 +67,23 @@
 <div><button type="submit">{{if .Suspension.Blocked}}Re-block{{else}}Block{{end}}</button></div>
 </form>
 </section>
+<section class="panel"><h2>Roles</h2>
+{{$id := .ID}}
+{{if .Roles}}
+<table class="list">
+<thead><tr><th>Role</th><th></th></tr></thead>
+<tbody>
+{{range .Roles}}
+<tr><td><code>{{.}}</code></td><td><form class="form" method="post" action="/_gm/users/{{$id}}/revoke-role"><input type="hidden" name="role" value="{{.}}"><button type="submit">Revoke</button></form></td></tr>
+{{end}}
+</tbody>
+</table>
+{{else}}<p class="note">no roles</p>{{end}}
+<form class="form col" method="post" action="/_gm/users/{{$id}}/grant-role">
+<label>Grant role <select name="role">{{range .KnownRoles}}<option value="{{.}}">{{.}}</option>{{end}}</select></label>
+<div><button type="submit">Grant</button></div>
+</form>
+</section>
 {{if .MoveChart}}
 <section class="panel"><h2>Move timing</h2>
 <p class="note">Think time per move number across all games — <span class="lg lg-min">min</span> · <span class="lg lg-avg">mean</span> · <span class="lg lg-max">max</span>.</p>