Fix documentation deployment to use gh-pages branch instead of GitHub Pages environment

[Copilot]

Problem

The documentation workflow was deploying to the GitHub Pages environment, which clutters the main branch deployment history. According to the issue, documentation should be deployed to the gh-pages branch while keeping the main branch clean for code review only.

Solution

Modified .github/workflows/docs.yml to deploy built documentation directly to the gh-pages branch using peaceiris/actions-gh-pages@v4 instead of the GitHub Pages environment.

Key Changes

• Deployment target: Changed from GitHub Pages environment to gh-pages branch
• Permissions: Simplified from contents: read, pages: write, id-token: write to contents: write
• Workflow structure: Consolidated from separate build/deploy jobs to single job with conditional deployment
• Deployment condition: Added github.event_name == 'push' to ensure deployment only on main branch pushes, not PRs

Benefits

• ✅ Clean main branch - only source code and documentation sources, no deployment artifacts
• ✅ PRs build documentation for validation but don't deploy
• ✅ Main branch pushes automatically deploy to gh-pages branch
• ✅ Documentation remains accessible at the same URL: https://rafnixg.github.io/bcv-api/
• ✅ Simplified workflow with better separation of concerns

Testing

• Validated YAML syntax and workflow structure
• Confirmed MkDocs build process works correctly
• Verified build artifacts are properly ignored via .gitignore

The workflow will now properly deploy documentation to the gh-pages branch while keeping the main branch focused on clean code review.

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