[Docs]: Refresh CONTRIBUTING.md with the real dev workflow

[shauryagangrade]

Problem

CONTRIBUTING.md describes pip install -e . only and says nothing about the
actual stack: uv sync, ruff, mypy, bandit, the CI matrix, or how to add a
new tool/slash command. New contributors can't validate their work locally
without reverse-engineering CI.

Proposed approach

• Document uv sync --extra dev setup and the exact check commands CI runs
  (ruff check, ruff format --check, mypy gcode, bandit, compileall).
• Add a "add a new tool / slash command" end-to-end checklist with the files
  involved (tools.py, TOOL_MAP, _SLASH_COMMANDS, _print_help, README).
• Link the good first issue and help wanted labels.

Where to look

• CONTRIBUTING.md
• .github/workflows/ci.yml:30-38
• gcode/ui.py:23-36 (_SLASH_COMMANDS), gcode/cli.py:33-55 (_print_help)

Acceptance criteria

• A newcomer can go from clone to green local checks using the doc alone.
• New-tool checklist is accurate against the current code.

Difficulty

Low — good first issue (docs).

[Rithikmahadev12]

I can update CONTRIBUTING.md to reflect the current workflow, adding the uv sync, linting, type‑checking and security‑scan commands along with a checklist for new tools based on the existing CI configuration. I would do this for a $10 USD estimate, provided the scope remains limited to the items described in the triage summary. Please confirm that this matches your expectations before I begin. I can have the changes ready within a day or two of receiving the go‑ahead.

[shauryagangrade]

Thanks for offering, but GCode is a volunteer-driven open-source project — we don't pay for contributions and don't outsource issues.

If you're interested, you're welcome to take on this issue for free as a normal contributor: it's labeled "good first issue", and CONTRIBUTING.md describes the workflow. A straightforward PR updating CONTRIBUTING.md would be welcome.

[aryansk]

I'll take this on — refreshing CONTRIBUTING.md with the real dev workflow (uv sync, the exact CI check commands, and a new-tool checklist) as the maintainer suggested.