feat: add multi-chain support to blockchain explorer and improve GPU review handling

- Add multi-chain configuration with devnet, testnet, and mainnet RPC URLs
- Add chain selector dropdown in explorer UI for network switching
- Add chain_id parameter to all API endpoints (chain/head, blocks, transactions, search)
- Add /api/chains endpoint to list supported blockchain networks
- Update blockchain explorer port from 3001 to 8016
- Update devnet RPC port from 8080 to 8026
- Add GPU reviews table

apps/coordinator-api/src/app/app.py

@@ -0,0 +1,5 @@
+# Import the FastAPI app from main.py for uvicorn compatibility
+import sys
+import os
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+from main import app