feat(v3.13.0): settings live DB reads, remove Directus/Appwrite, admin stats

Settings fixes:
- MAX_SITES_PER_USER, USER_RATE_LIMIT_PER_MIN/HR now read from DB settings
  table (DB > ENV > default), so dashboard/settings changes apply without
  restart. Sync cache refreshed on every save or delete.
- /api/me reports the live DB value for max_sites_per_user.

Admin improvements:
- Admin users bypass per-user rate limiting entirely (role=admin or ADMIN_EMAILS).
- Admin Overview now shows platform stats: registered users, new users (7d),
  total user sites, available tools.

Plugin cleanup:
- Appwrite and Directus plugins removed from the active registry (8 plugins
  now: WordPress, WooCommerce, WordPress Specialist, Gitea, n8n, Supabase,
  OpenPanel, Coolify). Plugin code is retained for future re-enabling.
- Settings page plugin visibility list updated to match.

Mobile onboarding:
- Stepper steps on narrow viewports stack vertically with correct full border
  and rounded corners on each step.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_site_api.py

@@ -80,17 +80,18 @@ class TestCredentialFields:
 
     @pytest.mark.unit
     def test_get_credential_fields_all_plugins(self):
-        """All 9 plugin types should return non-empty credential field lists."""
+        """Every registered plugin type returns non-empty credential field lists."""
         expected_plugins = [
             "wordpress",
             "woocommerce",
-            "wordpress_advanced",
+            "wordpress_specialist",
             "gitea",
             "n8n",
             "supabase",
             "openpanel",
             "appwrite",
             "directus",
+            "coolify",
         ]
         for plugin_type in expected_plugins:
             fields = get_credential_fields(plugin_type)
@@ -143,13 +144,13 @@ class TestCredentialValidation:
 
     @pytest.mark.unit
     def test_validate_credentials_optional_field(self):
-        """Optional fields (like container) should not cause errors when missing."""
+        """Optional advanced fields should not cause errors when missing."""
         valid, errors = validate_credentials(
-            "wordpress_advanced",
+            "wordpress",
             {
                 "username": "admin",
                 "app_password": "xxxx xxxx xxxx xxxx",
-                # container is optional — should not cause error
+                # wp_app_password is optional — should not cause error
             },
         )
         assert valid is True