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_models.py

@@ -89,6 +89,7 @@ def test_connection_rejects_bad_master():
 def test_pending_submission_defaults_to_pending_status():
     p = PendingSubmission(
         pending_id="p_1",
+        app_name="test-app",
         connection="prod",
         master="yarn",
         deploy_mode="cluster",
@@ -105,13 +106,14 @@ def test_pending_submission_defaults_to_pending_status():
     assert p.job_id is None
     assert p.application_id is None
     assert p.yarn_rm_url is None  # default for connections without one set
-    assert p.app_name is None
+    assert p.app_name == "test-app"
 
 
 def test_pending_submission_carries_yarn_rm_url_snapshot():
     """snapshotting yarn_rm_url lets prepare/confirm survive connection edits."""
     p = PendingSubmission(
         pending_id="p_x",
+        app_name="test-app",
         connection="prod",
         master="yarn",
         deploy_mode="cluster",
@@ -122,6 +124,7 @@ def test_pending_submission_carries_yarn_rm_url_snapshot():
         executor_cores=2,
         num_executors=2,
         spark_conf={},
+        extra_args={},
         created_at=datetime(2026, 6, 24),
     )
     assert p.yarn_rm_url == "http://rm-prod:8088"
@@ -130,6 +133,7 @@ def test_pending_submission_carries_yarn_rm_url_snapshot():
 def test_pending_submission_can_record_outcome():
     p = PendingSubmission(
         pending_id="p_2",
+        app_name="test-app",
         connection="prod",
         master="yarn",
         deploy_mode="cluster",
@@ -139,6 +143,7 @@ def test_pending_submission_can_record_outcome():
         executor_cores=2,
         num_executors=2,
         spark_conf={},
+        extra_args={},
         created_at=datetime(2026, 6, 24),
         status="SUBMITTED",
         job_id="j_abc",