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.

src/mcp_forge/execution/jupyter/backend.py

@@ -55,7 +55,9 @@ class JupyterBackend:
         memory: Optional[str] = None,
         cpu_quota: Optional[int] = None,
         custom_image: Optional[str] = None,
-        volumes: Optional[Dict[str, dict]] = None
+        volumes: Optional[Dict[str, dict]] = None,
+        injection_code: Optional[str] = None,
+        bridge_socket_path: Optional[str] = None
     ) -> ExecutionResult:
         """
         Execute code in stateful session.
@@ -71,6 +73,8 @@ class JupyterBackend:
             cpu_quota: CPU quota (uses config default if None)
             custom_image: Custom image name (uses config default if None)
             volumes: Volume mounts dict
+            injection_code: Optional MCP tool injection code (executed once at session start)
+            bridge_socket_path: Optional path to MCP bridge socket for mounting
         
         Returns:
             ExecutionResult with execution output and metadata
@@ -106,7 +110,7 @@ class JupyterBackend:
         try:
             self.session_manager.get_session(session_id)
         except SessionError:
-            # Session doesn't exist, create it
+            # Session doesn't exist, create it with MCP injection
             resource_limits = ResourceLimits(
                 memory=memory,
                 cpu_quota=cpu_quota,
@@ -117,7 +121,9 @@ class JupyterBackend:
             self.session_manager.create_session(
                 session_id=session_id,
                 resource_limits=resource_limits,
-                volumes=volumes
+                volumes=volumes,
+                injection_code=injection_code,
+                bridge_socket_path=bridge_socket_path
             )
         
         # Execute in session