add .env.example for blockchain node configuration

apps/blockchain-node/.env.example

@@ -1,9 +1,18 @@
-CHAIN_ID=ait-devnet
-DB_PATH=./data/chain.db
-RPC_BIND_HOST=127.0.0.1
-RPC_BIND_PORT=8080
-P2P_BIND_HOST=0.0.0.0
-P2P_BIND_PORT=7070
-PROPOSER_KEY=change_me
-MINT_PER_UNIT=1000
-COORDINATOR_RATIO=0.05
+# Blockchain Node Configuration
+chain_id=ait-devnet
+supported_chains=ait-devnet
+
+rpc_bind_host=0.0.0.0
+rpc_bind_port=8006
+
+p2p_bind_host=0.0.0.0
+p2p_bind_port=7070
+
+proposer_id=aitbc1-proposer
+
+# Gossip backend: use broadcast with Redis for cross-node communication
+gossip_backend=broadcast
+gossip_broadcast_url=redis://localhost:6379
+
+# Data
+db_path=./data/chain.db