feat(provisioning): admin game-signup mode setting, invite link option, staff self-create

Follow-ups from live testing:

- Game-account creation is now an admin Settings control (disabled / website /
  hybrid / game) instead of a hidden on/off flag. The site offers creation for
  website+hybrid; help text notes the shard's SignupMode (Bridge.cfg) has the final
  say. game_account_signup setting widened to a 4-value enum + validated on save.
- Invites: the accept link is ALWAYS returned and shown with a Copy button, and a
  "Email the invitation" toggle lets an admin create a link-only invite (no email)
  or email it. Backend takes sendEmail (default true) and always returns acceptUrl.
- Staff can create a game account from their own /admin/characters page too
  (POST /admin/shard/account → the shared createGameAccount controller), so the
  form is reachable in both the player and admin portals.

Note: the admin Houses view (/admin/houses) already worked; the earlier failure
was a stale Vite HMR state for the new route (needs a hard refresh).

Client build clean; server routes load; swagger regenerated.

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

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

@@ -35,6 +35,18 @@ const FIELDS = [
     ],
     fallback: 'disabled',
   },
+  {
+    key: 'game_account_signup',
+    label: 'Game-account creation',
+    help: 'Whether players can create a GAME account (for the game client) from the site. The game server’s own SignupMode (Bridge.cfg) must agree: website/hybrid accept site-created accounts, game refuses them. When enabled, a “Create a game account” form appears in the player portal.',
+    options: [
+      { value: 'disabled', label: 'Disabled — link an existing account only' },
+      { value: 'website', label: 'Website — the site creates game accounts' },
+      { value: 'hybrid', label: 'Hybrid — site or in-game (recommended)' },
+      { value: 'game', label: 'Game only — created in the game client, not the site' },
+    ],
+    fallback: 'disabled',
+  },
 ]
 
 export default function SettingsAdmin() {