feat(submit): update_pending_job tool for editing PENDING submissions

Add an update_pending_job MCP tool that lets callers modify parameters
of a PENDING submission before confirm_submit_job:
  - queue, executor_memory, executor_cores, num_executors
  - app_name
  - extra_args
  - script_path (re-validates file existence and SQL guard)

Only PENDING submissions can be updated; SUBMITTED/CANCELLED/FAILED are
rejected with HTTP 400.

spark_executor/tools/requests.py

@@ -75,6 +75,20 @@ class PendingIdRequest(BaseModel):
     pending_id: str
 
 
+class UpdatePendingJobRequest(BaseModel):
+    pending_id: str
+    script_path: str | None = Field(
+        default=None,
+        description="Optional new absolute path to the PySpark script. If provided, the file must exist and pass SQL guard.",
+    )
+    queue: str | None = None
+    executor_memory: str | None = None
+    executor_cores: int | None = None
+    num_executors: int | None = None
+    app_name: str | None = None
+    extra_args: dict[str, str] | None = None
+
+
 class JobIdRequest(BaseModel):
     job_id: str