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.

spark_executor/models.py

@@ -86,7 +86,7 @@ class Connection(BaseModel):
 
 class PendingSubmission(BaseModel):
     pending_id: str
-    app_name: str | None = None
+    app_name: str
     connection: str
     master: str
     deploy_mode: str
@@ -97,6 +97,7 @@ class PendingSubmission(BaseModel):
     executor_cores: int
     num_executors: int
     spark_conf: dict[str, str] = Field(default_factory=dict)
+    extra_args: dict[str, str] = Field(default_factory=dict)
     created_at: datetime
     status: str = "PENDING"  # PENDING | SUBMITTED | CANCELLED | FAILED
     error: str | None = None