Add --make-commit to cluv submit to auto-commit tracked changes before job submission

[Copilot]

cluv submit currently exits on dirty tracked changes. This PR adds an opt-in --make-commit path that creates a local commit before submission, and records the launched submit command in the commit body.

• CLI surface

  • Adds --make-commit to cluv submit.

• Submit flow changes

  • Extends submit(...) with make_commit: bool = False.
  • Keeps existing behavior unchanged when the flag is not used (dirty tracked repo still exits).
  • When --make-commit is enabled and tracked files are dirty:
    • stages tracked changes only via git add -u
    • creates a commit with:
      • subject: cluv submit: auto-commit tracked changes
      • body containing the launched submit command
  • Adds explicit error reporting for failures during auto-staging/auto-commit.

• Command capture semantics

  • Introduces a submit-command builder used for commit body content.
  • Stored command omits --make-commit to avoid recursive reuse behavior.

• Tests

  • Adds focused coverage for:
    • dirty repo exit behavior without --make-commit
    • auto-commit path with tracked-only staging
    • commit body command content
    • command reconstruction helper behavior
    • validation that make-commit path requires a command builder

# New opt-in behavior:
await submit(
    cluster="mila",
    job_script=Path("scripts/job.sh"),
    sbatch_args=["--time=00:10:00"],
    program_args=["python", "train.py"],
    make_commit=True,
)