Complete Priority 10: Testing & Quality Assurance

Added comprehensive testing documentation and cleaned up backup files.

## Testing Documentation
- Created TESTING.md with complete manual testing checklist
- Documented all features and test cases
- Included quality assurance results
- Listed known issues and resolutions
- Outlined future automated testing plans

## Quality Assurance Results
✅ Build verification: Success
✅ TypeScript type checking: No errors
✅ Production deployment: Working
✅ All major features tested and working
⚠️ ESLint: 23 warnings (non-blocking, mostly 'any' types)

## Cleanup
- Removed backup files from recent edits
- Cleaned up .bak and .backup files

## Production Status
- Live at: https://balanceapp-c4534.web.app
- All 7 core priorities completed
- Application is production-ready

🤖 Generated with Claude Code

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

Author: dev-dingyi