chore: standardize configuration, logging, and error handling across blockchain node and coordinator API

- Add infrastructure.md and workflow files to .gitignore to prevent sensitive info leaks
- Change blockchain node mempool backend default from memory to database for persistence
- Refactor blockchain node logger with StructuredLogFormatter and AuditLogger (consistent with coordinator)
- Add structured logging fields: service, module, function, line number
- Unify coordinator config with Database

docs/0_getting_started/2_installation.md

@@ -0,0 +1,71 @@
+# Installation
+
+## Prerequisites
+
+- Python 3.10+
+- Git
+- (Optional) PostgreSQL 14+ for production
+- (Optional) NVIDIA GPU + CUDA for mining
+
+## Monorepo Install
+
+```bash
+git clone https://github.com/oib/AITBC.git
+cd aitbc
+python -m venv .venv && source .venv/bin/activate
+pip install -e .
+```
+
+This installs the CLI, coordinator API, and blockchain node from the monorepo.
+
+## Environment Configuration
+
+### Coordinator API
+
+Create `apps/coordinator-api/.env`:
+```env
+JWT_SECRET=your-secret-key
+DATABASE_URL=sqlite:///./data/coordinator.db   # or postgresql://user:pass@localhost/aitbc
+LOG_LEVEL=INFO
+```
+
+### Blockchain Node
+
+Create `apps/blockchain-node/.env`:
+```env
+CHAIN_ID=ait-devnet
+RPC_BIND_HOST=0.0.0.0
+RPC_BIND_PORT=8080
+MEMPOOL_BACKEND=database
+```
+
+## Systemd Services (Production)
+
+```bash
+sudo cp systemd/aitbc-*.service /etc/systemd/system/
+sudo systemctl daemon-reload
+sudo systemctl enable --now aitbc-coordinator-api
+sudo systemctl enable --now aitbc-blockchain-node-1
+```
+
+## Verify
+
+```bash
+systemctl status aitbc-coordinator-api
+curl http://localhost:8000/v1/health
+aitbc blockchain status
+```
+
+## Troubleshooting
+
+| Problem | Fix |
+|---------|-----|
+| Port in use | `sudo lsof -i :8000` then `kill` the PID |
+| DB corrupt | `rm -f data/coordinator.db && python -m app.storage init` |
+| Module not found | Ensure venv is active: `source .venv/bin/activate` |
+
+## Next Steps
+
+- [3_cli.md](./3_cli.md) — CLI usage guide
+- [../2_clients/1_quick-start.md](../2_clients/1_quick-start.md) — Client quick start
+- [../3_miners/1_quick-start.md](../3_miners/1_quick-start.md) — Miner quick start