feat: add hot-swappable executor support for collections and agents

- Add executor configuration to Collection and Agent models in Prisma schema
- Create ExecutorConfigPanel component for selecting default or custom executors
- Add executor resolution logic with cascade (Agent → Collection → System Default)
- Create /api/executors/verify endpoint to test custom executor connectivity
- Add executor documentation page at /docs/executors with API specification
- Create deployable Vercel executor template in templates/vercel-executor/
- Update MCP handlers and agent tool execution to use configurable executors
- Add executor types and schemas to @tpmjs/types package

Users can now deploy their own executor instances and configure collections
or agents to use custom executors instead of the TPMJS default executor.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/types/package.json

@@ -36,6 +36,10 @@
     "./user": {
       "types": "./dist/user.d.ts",
       "default": "./dist/user.js"
+    },
+    "./executor": {
+      "types": "./dist/executor.d.ts",
+      "default": "./dist/executor.js"
     }
   },
   "files": ["dist"],