Add MCP injection support to Jupyter backend

- start_kernel() now accepts injection_code and bridge_socket_path
- Bridge Unix domain socket mounted as volume in container
- Injection code executed once on kernel startup (silent, no history)
- New _execute_injection_code() helper method with error handling
- Parameters passed through SessionManager.create_session()
- Parameters passed through JupyterBackend.execute()
- Updated JUPYTER_IMPLEMENTATION_STATUS.md

This mirrors the MCP injection pattern from the simple executor,
allowing MCP tools to be available in Jupyter sessions.

docs/JUPYTER_IMPLEMENTATION_STATUS.md

@@ -48,7 +48,14 @@
    - `cleanup_idle_kernels()`: Time-based cleanup
    - Activity timestamp updates
 
-6. **Dependencies**
+6. **MCP Integration**
+   - `start_kernel()` accepts `injection_code` and `bridge_socket_path`
+   - Bridge socket mounted as volume in container (Unix domain socket)
+   - Injection code executed once on kernel startup (silent, no history)
+   - Error handling for injection failures
+   - Passed through SessionManager and JupyterBackend
+
+7. **Dependencies**
    - `jupyter-client>=8.8.0` added to server dependencies
    - `ipykernel` removed from server (will be in container image)
    - `pyzmq>=27.1.0` for ZMQ support
@@ -57,6 +64,7 @@
    - [architecture1.md](../docs/architecture1.md) updated with Jupyter Backend section
    - [todo.md](../docs/todo.md) Phase 2.2.1 updated with architecture details
    - Architecture flow diagram and session mapping explanation
+   - [JUPYTER_IMPLEMENTATION_STATUS.md](../docs/JUPYTER_IMPLEMENTATION_STATUS.md) tracking document
 
 ### 🚧 In Progress / TODO