Slidesfly integrations v0.2.0

Marketplace-ready release for the Slidesfly publish Action.

• Adds the root action.yml entry required by GitHub Marketplace.
• Reuses this public integrations repository; no additional repository is required.
• Keeps actions/publish available for existing workflows.
• Pins both Action entry points to the deployed Slidesfly CLI 0.1.2.
• Adds CI drift checks for the root and legacy Action manifests.
• Verifies the root Action against the existing owned production test deck.

Use the root Action with:

- id: deck
  uses: rare/slidesfly-integrations@v0.2.0
  with:
    file: deck.html
    api-key: ${{ secrets.SLIDESFLY_API_KEY }}
    visibility: unlisted

Production smoke: https://github.com/rare/slidesfly-integrations/actions/runs/30512464640