feat(mcp): upgrade to StreamableHTTPServerTransport

- Replace deprecated SSEServerTransport with StreamableHTTPServerTransport
- Update MCP SDK to v1.25.3
- Add /mcp endpoint for unified HTTP transport
- Maintain legacy /sse and /message redirects for compatibility

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jonathanpeterwu