feat(backend): add standalone data plane

Replace the Supabase application data plane with the Node/PostgreSQL API, migrate mobile, admin, web, and MCP callers, add controlled cutover tooling, and define hardened Dokploy infrastructure.

apps/mcp/.env.example

@@ -1,4 +1,7 @@
-PORT=3000
-SUPABASE_URL=https://your-project.supabase.co
-SUPABASE_SERVICE_ROLE_KEY=your-service-role-key
+PORT=3002
+# Standalone admin API only. The token maps to ADMIN_API_SERVICE_USER_ID inside
+# the API; MCP must not receive that UUID, a database URL, or a Supabase key.
+SAUCI_ADMIN_API_URL=http://127.0.0.1:3003
+SAUCI_ADMIN_API_TOKEN=use-a-separate-32-character-service-token
+# Independent caller-facing authentication for the MCP HTTP service.
 SAUCI_MCP_API_KEY=your-secret-api-key