Add browser testing HTML page and POC README

test.html:
- Manual browser testing interface with visual results
- System information display (OPFS/IndexedDB detection)
- Test suites: Basic, CRUD, Transactions, Graph operations
- Performance metrics and statistics
- Clear, actionable UI for validation

README.md:
- Complete POC documentation and setup instructions
- Architecture overview and project structure
- Testing strategy (Node.js vs browser)
- VFS comparison table and usage examples
- Next steps and known limitations

Enables manual validation of BrowserAdapter in browser environment.
Run with: npx http-server . -p 8080 && open test.html

Status: Ready for browser testing ✅

Author: michaeloboyle