feat(skills): replace lifecycle skills with copilotkit-* from CopilotKit/skills

- Remove 6 old auto-generated lifecycle skills (0-to-working-chat,
  debug-and-troubleshoot, go-to-production, scale-to-multi-agent,
  spa-without-runtime, v1-to-v2-migration)
- Add 8 canonical skills verbatim from github.com/CopilotKit/skills:
  copilotkit-setup, copilotkit-develop, copilotkit-agui,
  copilotkit-integrations, copilotkit-debug, copilotkit-upgrade,
  copilotkit-contribute, copilotkit-self-update
- Update copilotkit-self-update install command to reference CopilotKit/CopilotKit
- Add .claude-plugin/{plugin,marketplace}.json and .mcp.json (repo URL and
  version updated to match monorepo: CopilotKit/CopilotKit, v1.57.3)
- Exempt copilotkit-* slugs from sync orphan detection in sync-plugin-skills.ts;
  runtime/react-core/a2ui-renderer remain synced from packages/*/skills as before

.mcp.json

@@ -1,9 +1,8 @@
 {
   "mcpServers": {
-    "nx-mcp": {
-      "type": "stdio",
-      "command": "npx",
-      "args": ["nx", "mcp"]
+    "copilotkit-docs": {
+      "type": "http",
+      "url": "https://mcp.copilotkit.ai/mcp"
     }
   }
 }