fix: add write permissions to gh-pages workflow

Add contents: write, pages: write, and id-token: write permissions
to fix 403 error when pushing to gh-pages branch.

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

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

.github/workflows/gh-pages-fast.yml

@@ -12,6 +12,10 @@ on:
 jobs:
   build-deploy:
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pages: write
+      id-token: write
     steps:
     - uses: actions/checkout@v4