fix(devtools): stabilize Penpot MCP, fix S3 creds, OIDC registration

MCP server:
- Replace vite build --watch + livePreview with static vite preview
  (watch mode was reloading the plugin iframe, killing WebSocket)
- Bake WS_URI at Docker build time for production WebSocket URL
- Add server-side application-level keepalive messages every 25s
- Add client-side auto-reconnect with exponential backoff
- Set Pingora route timeout to 86400s for WebSocket idle tolerance

Penpot:
- Add AWS_ACCESS_KEY_ID/SECRET env vars for S3 SDK compatibility
- Set S3 region to satisfy AWS SDK credential chain
- Enable OIDC registration (disable-registration blocks OIDC signup)
- Fix frontend port (8080 not 80)
- Add penpot bucket to seaweedfs-buckets init job

base/data/postgres-cluster.yaml

@@ -46,6 +46,8 @@ spec:
         - CREATE DATABASE find_db OWNER find;
         - CREATE USER penpot WITH LOGIN;
         - CREATE DATABASE penpot_db OWNER penpot;
+        - CREATE USER stalwart WITH LOGIN;
+        - CREATE DATABASE stalwart_db OWNER stalwart;
 
   storage:
     size: 10Gi