* 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
