refactor: merge .env.production into central .env and standardize paths

- Merge blockchain-node/.env.production into central /opt/aitbc/.env
- Update all blockchain paths to use standardized /var/lib/aitbc/ structure
- Remove separate .env.production file (merged into central config)
- Update systemd services to remove references to .env.production
- Standardize Coordinator API paths and RPC port (8006)
- Add trusted_proposers setting for follower nodes
- Update multi-node workflow to reflect merged configuration
- Use aitbc1genesis as default proposer in central .env
- All services now use single central .env file with standardized paths

This eliminates configuration file duplication and ensures consistent
directory structure across all AITBC services.

systemd/aitbc-blockchain-node.service

@@ -10,7 +10,6 @@ WorkingDirectory=/opt/aitbc/apps/blockchain-node
 EnvironmentFile=/opt/aitbc/.env
 Environment=PATH=/usr/bin:/usr/local/bin:/usr/bin:/bin
 Environment=PYTHONPATH=/opt/aitbc/apps/blockchain-node/src:/opt/aitbc/apps/blockchain-node/scripts
-EnvironmentFile=/opt/aitbc/apps/blockchain-node/.env.production
 ExecStart=/opt/aitbc/venv/bin/python -m aitbc_chain.combined_main
 Restart=always
 RestartSec=5