docs: Add comprehensive documentation for new features

1. resilience.md - Production resilience guide
   - Retry strategies and exponential backoff
   - Rate limiting and back pressure
   - Error classification and handling
   - Configuration best practices
   - Real-world scenarios and tuning

2. SNOWFLAKE_LOADER_GUIDE.md - Snowflake loader guide
   - All loading methods comparison (stage, insert, pandas, streaming)
   - State management and resume capability
   - Label joining for data enrichment
   - Performance tuning and optimization
   - Parallel loading configuration
   - Reorg handling strategies
   - Troubleshooting common issues

3. snowflake_loader.md - API reference placeholder

Author: fordN