feat(submit): require explicit confirmation for all prepare_submit_job params

Remove defaults from queue, executor_memory, executor_cores,
num_executors, and app_name in prepare_submit_job. All must now be
explicitly confirmed by the caller.

Also add extra_args to the PendingSubmission snapshot so users can
confirm non-conf spark-submit flags (e.g. --jars, --py-files) at
prepare time; confirm_submit_job passes them through to
build_spark_submit_command.

This is an intentional breaking change to the MCP tool contract:
callers can no longer rely on implicit defaults.

tests/unit/test_requests.py

@@ -0,0 +1,23 @@
+# coding=utf-8
+import pytest
+
+from spark_executor.tools.requests import PrepareSubmitJobRequest
+
+
+def test_prepare_submit_job_request_requires_all_confirmed_parameters():
+    with pytest.raises(ValueError):
+        PrepareSubmitJobRequest(connection="prod", script_path="/tmp/x.py")
+
+
+def test_prepare_submit_job_request_accepts_extra_args():
+    req = PrepareSubmitJobRequest(
+        connection="prod",
+        script_path="/tmp/x.py",
+        queue="default",
+        executor_memory="4G",
+        executor_cores=2,
+        num_executors=2,
+        app_name="test-app",
+        extra_args={"jars": "hdfs:///lib/foo.jar"},
+    )
+    assert req.extra_args == {"jars": "hdfs:///lib/foo.jar"}