```

chore: remove obsolete files and add Solidity build artifacts to .gitignore

- Add ignore patterns for Solidity build artifacts (typechain-types, artifacts, cache)
- Remove unused exchange mock API server (api/exchange_mock_api.py)
- Remove obsolete client-web README placeholder
- Remove deprecated marketplace-ui HTML implementation
```

configs/systemd/aitbc-miner.service

@@ -1,25 +0,0 @@
-[Unit]
-Description=AITBC Miner Node
-After=network-online.target
-Wants=network-online.target
-
-[Service]
-Type=simple
-User=aitbc
-Group=aitbc
-WorkingDirectory=/opt/aitbc/apps/miner-node
-EnvironmentFile=/opt/aitbc/apps/miner-node/.env
-ExecStart=/opt/aitbc/apps/miner-node/.venv/bin/python -m aitbc_miner.main
-Restart=always
-RestartSec=3
-Nice=5
-IOSchedulingClass=best-effort
-IOSchedulingPriority=6
-NoNewPrivileges=true
-PrivateTmp=true
-ProtectSystem=full
-ProtectHome=true
-ReadWritePaths=/opt/aitbc/apps/miner-node /var/log/aitbc
-
-[Install]
-WantedBy=multi-user.target