Restore the main.yml Actions badge target

[Copilot]

The README references the GitHub Actions badge for .github/workflows/main.yml, but that workflow file was no longer a valid Actions definition. This change restores main.yml as a real workflow so the badge resolves against an actual pipeline again.

• Workflow restoration

  • Replaced the invalid contents of .github/workflows/main.yml with a valid GitHub Actions workflow named Main
  • Scoped triggers to the repository’s default branch, Main
  • Kept the job minimal and aligned with the repository’s existing build path

• README badge

  • Added the requested badge snippet at the top of README.md
  • Pointed both the badge image and link at actions/workflows/main.yml

• Resulting workflow shape

  name: Main
  
  on:
    push:
      branches:
        - Main
    pull_request:
      branches:
        - Main
    workflow_dispatch:
  
  jobs:
    build:
      runs-on: ubuntu-latest
      steps:
        - uses: actions/checkout@v4
        - uses: actions/setup-node@v4
          with:
            node-version: 20
        - run: npm run build

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