Fix playground CORS by deploying to gh-pages branch

Problem: GitHub Releases don't serve files with CORS headers, blocking
browser fetch() requests. CORS proxies are unreliable for large files.

Solution: Deploy playground to gh-pages branch with WASM files included.
- Main branch stays clean (no 63MB WASM files)
- Workflow downloads WASM from latest release
- Pushes to separate gh-pages branch (orphan, separate history)
- GitHub Pages serves with proper CORS headers
- Same-origin = no CORS issues

Changes:
- Updated deploy workflow to download WASM and push to gh-pages
- Simplified index.html to use local files (served via Pages)
- Added clangd files to .gitignore
- Added ?prod=1 URL param for local testing

Author: cs01

.github/workflows/deploy-playground.yml

@@ -64,6 +64,9 @@ jobs:
           mv nullsafe-playground/* .
           rm -rf nullsafe-playground
 
+          # Disable Jekyll processing
+          touch .nojekyll
+
           # Add all files (including the downloaded WASM)
           git add -A