Fix docs deployment from tag triggers

Always checkout master branch in the docs workflow, even when triggered
by a tag push. This ensures GitHub Pages accepts the deployment since
it's configured with source.branch: master.

sphinx-multiversion still builds all versions (tags + master) because
fetch-depth: 0 fetches all refs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: laughingman7743

.github/workflows/docs.yaml

@@ -24,7 +24,8 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
         with:
-          fetch-depth: 0  # Fetch all history for version detection
+          ref: master  # Always checkout master for GitHub Pages deployment
+          fetch-depth: 0  # Fetch all history for sphinx-multiversion
       - name: Setup Pages
         uses: actions/configure-pages@v5
       - uses: astral-sh/setup-uv@v5