[Tracking]: Spark Client Batch Jobs, Lifecycle Management, Observability, and Production Readiness

# Tracking Issue: Spark Client Batch Jobs, Lifecycle Management, Observability, and Production Readiness

## Overview

This tracking issue tracks implementation work for Spark batch jobs, lifecycle management, observability, testing, documentation, and production readiness for the Spark Client.

Related:
- KEP-107: Spark Client

## Design & Proposal

- [x] SparkClient long-running job submission proposal (extends KEP-107) #524

## Implementation

### Batch Job Submission

- [x] FileJob-based batch job submission, lifecycle management APIs, and unit tests (`submit_job()`, `list_jobs()`, `get_job()`, `wait_for_job_status()`, `delete_job()`, `get_job_logs()`) #521
- [x] FuncJob support (`submit_job(job=FuncJob(...))`) #629
- [x] `spark_conf` support for SparkApplication jobs #646
- [x] `options` support for SparkApplication jobs #685

### Testing & Validation

- [x] Unit and e2e test coverage — included in each feature PR

### Documentation & Examples

- [x] SparkClient batch jobs documentation and examples #730
- [x] Kubeflow blog post: "Batch Jobs for SparkClient" https://github.com/kubeflow/blog/pull/207

Start with KEP-107 and the linked implementation issues #521, #629, #646, #685, and #730. The tracking issue shows all listed work as complete, including tests and documentation, so confirm whether any new production-readiness task remains before attempting changes.

Written by the indexing model from the issue text.