Stop tracking slurm_jobs/ (local job scripts + logs)

Untrack the slurm_jobs/ directory and add it to .gitignore; these are
per-machine job scripts and SLURM .out/.err logs, not source. Files are
kept on disk.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Donglai Wei

.gitignore

@@ -160,3 +160,4 @@ dev/
 .codex
 .claude
 .agent/
+slurm_jobs/