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>

env.example

@@ -34,6 +34,15 @@ DASHBOARD_SESSION_SECRET=
 # Admin users always see all plugins regardless of this setting.
 # Default (if not set): wordpress,woocommerce,supabase,openpanel,gitea
 # ENABLED_PLUGINS=wordpress,woocommerce,supabase,openpanel,gitea
+#
+# Plugin notes:
+#   wordpress_specialist — F.19 specialist tool surface (51 tools across
+#       read / editor / settings / install / admin tiers). Companion-
+#       backed (Airano MCP Bridge v2.18.0+ on the WP side). No Docker
+#       socket needed. Currently admin-only; will become public with
+#       a tier system in F.19.4 (companion v3.0 wp.org republish).
+#       Replaced the deprecated wordpress_advanced plugin (sunset
+#       2026-05-04 in F.19.3.2-.3).
 
 # ============================================
 # ADMIN SYSTEM (Track F.4)