- Add DataLayer, MockDataGenerator, RealDataFetcher, and get_data_layer to aitbc package exports
- Migrate blockchain-explorer/main.py to use aitbc.get_data_layer for mock/real data toggle
- Add data layer integration to search_transactions, search_blocks, and analytics_overview endpoints
- Migrate CLI blockchain commands to use chain registry instead of hardcoded chain list
- Replace hardcoded ['ait-devnet', 'ait-testnet'] with get