SPARC Phase 3-5: Complete BrowserAdapter implementation

Implementation:
- Complete BrowserAdapter class with VFS auto-selection
- BrowserStatement with proper parameter binding (1-indexed)
- Statement reuse pattern with automatic reset()
- Transaction management with automatic rollback
- Error handling with context enrichment
- Helper methods: bindParameters(), extractRow()
- Type-safe parameter binding for all SQLite types
- Diagnostic getVFS() method for debugging

Architecture highlights:
- OPFS > IndexedDB > memory VFS selection
- Interface parity with NodeAdapter (drop-in replacement)
- Proper resource cleanup (idempotent finalize/close)
- Comprehensive error messages for debugging

Documentation:
- Complete POC summary with findings and recommendations
- Integration examples and usage patterns
- Performance expectations for each VFS
- Risk assessment and next steps

Testing status:
- Implementation complete ✅
- Requires browser test environment (Playwright/Vitest)
- All 19 interface tests need browser validation

Next: Browser test setup and validation

Author: michaeloboyle