feat(provisioning): provisioning UI — signup, invites, accept page, unlink

Phase 6: the UI for the Phase 5 provisioning backend.

- CreateGameAccountForm: reusable game-account form (own username + password),
  mapping the sidecar errors (409/429/403/503) to friendly messages. Wired into
  GameAccounts (self-serve) — shown alongside the [link flow when the
  game_account_signup flag is on (exposed via public settings), so a registered
  player can create + link a game account from their portal.
- Admin Invites view (/admin/invites, admin-only): send an invite at a chosen
  access level, list invites with status, revoke pending ones. When email isn't
  configured the create response's accept link is surfaced to copy manually.
- Public accept page (/invite/:token): validates the invite, sets username +
  password (email + role pre-assigned), creates the account at that role and logs
  in; for a player invite it then offers the built-in "create game account" step
  before the portal. Honeypot-guarded like registration.
- Admin unlink wired into UserDetail via GameAccounts (per-account Unlink button,
  confirm + reconcile).
- Backend: expose gameAccountSignup availability in public settings.

Client build clean; server 193/193.

Refs .plans/protocol2-integration.md (Phase 6). Completes the Protocol 2.0/2.1 integration.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/src/App.jsx

@@ -46,6 +46,7 @@ import AdminCharacter from './routes/admin/views/AdminCharacter.jsx'
 import AuthProvidersAdmin from './routes/admin/views/AuthProvidersAdmin.jsx'
 import UsersAdmin from './routes/admin/views/UsersAdmin.jsx'
 import UserDetail from './routes/admin/views/UserDetail.jsx'
+import InvitesAdmin from './routes/admin/views/InvitesAdmin.jsx'
 import AccountAdmin from './routes/admin/views/AccountAdmin.jsx'
 import Moderation from './routes/admin/views/Moderation.jsx'
 import ModerationUser from './routes/admin/views/ModerationUser.jsx'
@@ -53,6 +54,7 @@ import ModerationUser from './routes/admin/views/ModerationUser.jsx'
 // Player portal
 import PlayerLogin from './routes/player/PlayerLogin.jsx'
 import PlayerRegister from './routes/player/PlayerRegister.jsx'
+import AcceptInvite from './routes/player/AcceptInvite.jsx'
 import PlayerPortalLayout from './routes/player/PlayerPortalLayout.jsx'
 import PlayerCharacters from './routes/player/PlayerCharacters.jsx'
 import PlayerCharacter from './routes/player/PlayerCharacter.jsx'
@@ -147,6 +149,7 @@ export default function App() {
             <Route path="auth-providers" element={<AuthProvidersAdmin />} />
             <Route path="users" element={<UsersAdmin />} />
             <Route path="users/:id" element={<UserDetail />} />
+            <Route path="invites" element={<InvitesAdmin />} />
             <Route path="account" element={<AccountAdmin />} />
             <Route path="*" element={<Navigate to="/admin" replace />} />
           </Route>
@@ -154,6 +157,7 @@ export default function App() {
           {/* Player portal */}
           <Route path="/account/login" element={<PlayerLogin />} />
           <Route path="/account/register" element={<PlayerRegister />} />
+          <Route path="/invite/:token" element={<AcceptInvite />} />
           <Route
             element={
               <RequirePlayer>