feat: make MCP SDK a peer dependency (#168)

* feat: make MCP SDK a peer dependency

- Move @modelcontextprotocol/sdk from dependencies to peerDependencies (^1.20.0)
- Add to devDependencies for local development (^1.24.3)
- Externalize SDK from all build entry points (app, app-bridge, react, server)

Benefits:
- Consumers control their SDK version
- Deduplication when consumer already has SDK
- Follows pattern of react/zod peer deps

* fix: require SDK ^1.24.0 for Zod 4 compatibility

Earlier SDK versions have Zod type incompatibilities that cause build errors.

* chore: update examples to SDK ^1.24.0 to match peer dep

examples/basic-server-react/package.json

@@ -12,7 +12,7 @@
   },
   "dependencies": {
     "@modelcontextprotocol/ext-apps": "../..",
-    "@modelcontextprotocol/sdk": "^1.22.0",
+    "@modelcontextprotocol/sdk": "^1.24.0",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
     "zod": "^4.1.13"