fix: replace deprecated Node.js 20 actions in draw workflow

[Copilot]

GitHub is deprecating Node.js 20 actions (forced June 2, 2026; removed September 16, 2026). The draw.yml workflow triggered this via the external reusable workflow caksoylar/keymap-drawer/.github/workflows/draw-zmk.yml@main, which uses actions/checkout@v4 and stefanzweifel/git-auto-commit-action@v5 — both Node.js 20. Since env vars don't propagate to called reusable workflows, the only fix is to own the steps directly.

Changes

• Inlined draw-zmk.yml logic into draw.yml, replacing the uses: caksoylar/keymap-drawer/... reusable workflow call with explicit steps
• Updated actions to Node.js 24 equivalents:
  • actions/checkout@v4 → actions/checkout@v6
  • stefanzweifel/git-auto-commit-action@v5 → stefanzweifel/git-auto-commit-action@v7
• Simplified the draw script to remove unused input handling (parse_args, draw_args, extra_keymap_yaml, amend_commit, etc.) since we were using defaults for all of them

build.yml is unaffected — zmkfirmware/zmk's reusable workflow already uses actions/checkout@v6.