feat: add weekly devbox update workflow

[abueide]

Summary

Add automated weekly workflow to keep devbox packages up-to-date using the xiaolutech/devbox-update-action.

Changes

• Add .github/workflows/devbox-update.yml workflow
• Runs weekly on Mondays at 10am UTC
• Can be manually triggered via workflow_dispatch
• Reusable via workflow_call for other repos

Why

Automates devbox package maintenance - checks for outdated packages via Devbox Search API and creates PRs with updates to both devbox.json and devbox.lock.

How It Works

The action:

1. Scans devbox.json for packages
2. Checks Devbox Search API for latest versions
3. Updates devbox.json and regenerates devbox.lock
4. Creates/updates PR with changes

Usage in Other Repos

This workflow is reusable, but it's simple enough to just copy to other repos:

name: Devbox Update
on:
  schedule:
    - cron: '0 10 * * 1'
  workflow_dispatch:
jobs:
  update:
    runs-on: ubuntu-latest
    permissions:
      contents: write
      pull-requests: write
    steps:
      - uses: actions/checkout@v4
      - uses: jetify-com/devbox-install-action@v0.14.0
      - uses: xiaolutech/devbox-update-action@v1
        with:
          token: \${{ secrets.GITHUB_TOKEN }}

Setup Required

Repository settings must have "Allow GitHub Actions to create and approve pull requests" enabled.

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