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/devtools/penpot-mcp.yaml

@@ -25,6 +25,8 @@ spec:
               containerPort: 4401
             - name: ws
               containerPort: 4402
+            - name: plugin
+              containerPort: 4400
           env:
             - name: PENPOT_MCP_REMOTE_MODE
               value: "true"
@@ -32,6 +34,10 @@ spec:
               value: "0.0.0.0"
             - name: PENPOT_MCP_SERVER_ADDRESS
               value: "mcp-designer.DOMAIN_SUFFIX"
+            - name: WS_URI
+              value: "wss://mcp-designer.DOMAIN_SUFFIX/ws"
+            - name: PENPOT_MCP_PLUGIN_SERVER_HOST
+              value: "0.0.0.0"
           resources:
             requests:
               cpu: 50m
@@ -54,3 +60,6 @@ spec:
     - name: ws
       port: 4402
       targetPort: ws
+    - name: plugin
+      port: 4400
+      targetPort: plugin