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/tools/requests.py

@@ -33,9 +33,9 @@ class SaveConnectionRequest(BaseModel):
 
 class PrepareSubmitJobRequest(BaseModel):
     connection: str
-    app_name: str | None = Field(
-        default=None,
-        description="Optional human-readable application name for tracking the pending submission.",
+    app_name: str = Field(
+        ...,
+        description="Human-readable application name for tracking the pending submission.",
     )
     script_path: str = Field(
         ...,
@@ -49,10 +49,26 @@ class PrepareSubmitJobRequest(BaseModel):
             "if the path is missing or not a file."
         ),
     )
-    queue: str = "default"
-    executor_memory: str = "4G"
-    executor_cores: int = 2
-    num_executors: int = 2
+    queue: str = Field(
+        ...,
+        description="YARN queue to submit to. Must be explicitly confirmed by the caller.",
+    )
+    executor_memory: str = Field(
+        ...,
+        description="Executor memory, e.g. '4G'. Must be explicitly confirmed by the caller.",
+    )
+    executor_cores: int = Field(
+        ...,
+        description="Number of cores per executor. Must be explicitly confirmed by the caller.",
+    )
+    num_executors: int = Field(
+        ...,
+        description="Total number of executors. Must be explicitly confirmed by the caller.",
+    )
+    extra_args: dict[str, str] | None = Field(
+        default=None,
+        description="Additional spark-submit flags (e.g. jars, py-files) confirmed at prepare time.",
+    )
 
 
 class PendingIdRequest(BaseModel):