chore: remove admin SPA and update to two-app production setup

Remove apps/admin/ entirely — platform admin functionality now lives
in apps/app/ under /platform/* routes for super_admin users.

Production URL scheme changed:
- Organizer app: crewli.app (was app.crewli.app)
- Portal: portal.crewli.app (unchanged)
- API: api.crewli.app (unchanged)
- admin.crewli.app and app.crewli.app retired

Backend:
- Removed FRONTEND_ADMIN_URL config and admin cookie (crewli_admin_token)
  from SetAuthCookie, CookieBearerToken, cors.php, app.php
- Updated .env and .env.example (two origins, no port 5173)
- Updated cookie test: admin origin test → unknown origin fallback test

Infrastructure:
- Makefile: removed admin target
- deploy/nginx: updated CSP comment, removed admin vhost
- Updated README.md, CLAUDE.md, and all dev-docs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/Http/Controllers/Api/V1/Traits/SetAuthCookie.php

@@ -10,7 +10,6 @@ use Symfony\Component\HttpFoundation\Cookie;
 trait SetAuthCookie
 {
     private const COOKIE_MAP = [
-        'admin' => 'crewli_admin_token',
         'app' => 'crewli_app_token',
         'portal' => 'crewli_portal_token',
     ];
@@ -23,14 +22,9 @@ trait SetAuthCookie
             ?? $request->headers->get('Referer')
             ?? '';
 
-        $adminUrl = config('app.frontend_admin_url', 'http://localhost:5173');
         $appUrl = config('app.frontend_app_url', 'http://localhost:5174');
         $portalUrl = config('app.frontend_portal_url', 'http://localhost:5175');
 
-        if ($this->originMatches($origin, $adminUrl)) {
-            return self::COOKIE_MAP['admin'];
-        }
-
         if ($this->originMatches($origin, $appUrl)) {
             return self::COOKIE_MAP['app'];
         }