feat: add --json output flag to submit, list, and report commands

[183amir]

Summary

• Add --json flag to submit, list, and report commands for machine-readable output
• --json is mutually exclusive with --wrap and --truncate on list
• Document --json flag in README

Examples

$ gridtk submit --json --wrap=echo hello
{"job_id": 1, "slurm_id": 42611, "name": "gridtk"}

$ gridtk list --json
[
  {
    "job_id": 1,
    "slurm_id": 42611,
    "state": "COMPLETED",
    "exit_code": "0",
    "name": "gridtk",
    ...
  }
]

$ gridtk report --json -j 1
[
  {
    "job_id": 1,
    "name": "gridtk",
    "state": "COMPLETED",
    "output_files": [{"path": "logs/gridtk.42611.out", "content": "hello\n"}]
  }
]

🤖 Generated with Claude Code

---

📚 Documentation preview 📚: https://gridtk--29.org.readthedocs.build/en/29/

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
src/gridtk
cli.py					475, 496-497, 673-678, 681-729
Project Total

This report was generated by python-coverage-comment-action

[Yannick-Dayer]

Cool feature.
Everything seems good 👍🏻