Add moderation dashboard, user history & notes (Phase 6a)

Surface the Discord bot's moderation data on the admin panel: a read-only
staff dashboard over the existing mod_actions log, per-user history, staff
notes, and a new moderator role. No bot changes.

Schema
- users.role ENUM gains 'moderator' (CREATE + idempotent ALTER for existing DBs)
- new server-owned mod_notes table (staff_only/admin_only visibility)

Server
- model/moderation: read mod_actions via the shared pool (documented read-only
  cross of the bot/server ownership boundary), correlate accounts through
  user_identities (provider='discord'), flag automated actions via
  staff_user_id === bot_config.application_id; pure reshaping helpers isolated
  in moderation.pure.js so they unit-test without opening a DB pool
- model/modNotes: list/add with role-gated admin_only visibility
- admin/moderation.controller + routes under /api/v1/admin/moderation/* gated by
  requireRole('admin','moderator'); admin_only note writes require admin
- allow assigning 'moderator' in the user create/update validators

Client
- /admin/moderation overview (window tiles, type-filterable recent feed, user
  lookup) and /user/:discordId history (tabs + notes with add-note)
- RoleGate; AdminLayout filters nav and confines moderators to their section
- moderator badge + action-type/auto badges

Deferred (see plan): 6b bot event capture (joins/leaves/filter/spam), 6c appeals
(needs public accounts), 6d /internal/mod-reverse bot reversal callback.

Verified: 116 server unit tests, client build, DB-backed model smoke, full
HTTP/RBAC e2e, and a browser click-through of the dashboard.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019rao86n5cXpwAyjdBFEshV

client/src/routes/admin/views/UsersAdmin.jsx

@@ -5,6 +5,8 @@ import { dateTime } from '../../../lib/format.js'
 import { api } from '../../../api/client.js'
 import UserEditor from './UserEditor.jsx'
 
+const ROLE_BADGE = { admin: 'badge-admin', editor: 'badge-editor', moderator: 'badge-moderator' }
+
 export default function UsersAdmin() {
   const [tick, setTick] = useState(0)
   const reload = useCallback(() => setTick((t) => t + 1), [])
@@ -16,7 +18,7 @@ export default function UsersAdmin() {
     <section>
       <div style={{ display: 'flex', alignItems: 'center', justifyContent: 'space-between', marginBottom: 18, flexWrap: 'wrap', gap: 12 }}>
         <p className="sans muted" style={{ margin: 0, fontSize: '0.9rem' }}>
-          Manage admin and editor accounts
+          Manage admin, editor, and moderator accounts
         </p>
         <button onClick={() => setEditing('new')} className="btn btn-primary btn-sq">
           + Add user
@@ -44,7 +46,7 @@ export default function UsersAdmin() {
                     {u.username}
                   </td>
                   <td className="adm-td">
-                    <span className={`badge ${u.role === 'admin' ? 'badge-admin' : 'badge-editor'}`}>{u.role}</span>
+                    <span className={`badge ${ROLE_BADGE[u.role] || 'badge-editor'}`}>{u.role}</span>
                   </td>
                   <td className="adm-td dim">{u.last_login_at ? dateTime(u.last_login_at) : 'never'}</td>
                   <td className="adm-td" style={{ textAlign: 'right' }}>