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/Middleware/CookieBearerToken.php

@@ -11,7 +11,6 @@ use Symfony\Component\HttpFoundation\Response;
 final class CookieBearerToken
 {
     private const COOKIE_NAMES = [
-        'crewli_admin_token',
         'crewli_app_token',
         'crewli_portal_token',
     ];
@@ -59,7 +58,6 @@ final class CookieBearerToken
         $originPort = parse_url($origin, PHP_URL_PORT);
 
         $map = [
-            'admin' => [config('app.frontend_admin_url', 'http://localhost:5173'), 'crewli_admin_token'],
             'app' => [config('app.frontend_app_url', 'http://localhost:5174'), 'crewli_app_token'],
             'portal' => [config('app.frontend_portal_url', 'http://localhost:5175'), 'crewli_portal_token'],
         ];