Add CI job to auto-update Homebrew cask on release

[fernandotonon]

Summary

• Add update-homebrew-cask job to the deploy workflow
• Automatically updates the Homebrew cask after macOS DMG is uploaded to a release
• Downloads the DMG, calculates SHA256, and updates the cask file in homebrew-qtmesheditor repo

How it works

1. Runs after build-macos job completes (only on release publish)
2. Downloads the DMG from the GitHub release
3. Calculates the SHA256 hash
4. Clones the homebrew-qtmesheditor repo
5. Updates version and sha256 in Casks/qtmesheditor.rb
6. Commits and pushes the changes

Setup Required

Create a GitHub secret named HOMEBREW_TAP_TOKEN:

1. Go to Settings → Secrets and variables → Actions
2. Create a new secret with a GitHub PAT that has repo scope
3. The PAT needs write access to fernandotonon/homebrew-qtmesheditor

Test plan

• Create a test release to verify the workflow runs correctly
• Verify the Homebrew cask is updated with correct version and SHA256

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