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/4_blockchain/6_networking.md

@@ -0,0 +1,107 @@
+# Networking Configuration
+Configure P2P networking for your blockchain node.
+
+## Network Settings
+
+### Firewall Configuration
+
+```bash
+# Allow P2P port
+sudo ufw allow 7070/tcp
+
+# Allow RPC port
+sudo ufw allow 8080/tcp
+
+# Allow from specific IPs
+sudo ufw allow from 10.0.0.0/8 to any port 8080
+```
+
+### Port Forwarding
+
+If behind a NAT, configure port forwarding:
+- External port 7070 → Internal IP:7070
+- External port 8080 → Internal IP:8080
+
+## Bootstrap Nodes
+
+### Default Bootstrap Nodes
+
+```yaml
+p2p:
+  bootstrap_nodes:
+    - /dns4/node-1.aitbc.com/tcp/7070/p2p/12D3KooW...
+    - /dns4/node-2.aitbc.com/tcp/7070/p2p/12D3KooW...
+    - /dns4/node-3.aitbc.com/tcp/7070/p2p/12D3KooW...
+```
+
+### Adding Custom Bootstrap Nodes
+
+```bash
+aitbc-chain p2p add-bootstrap /dns4/my-node.example.com/tcp/7070/p2p/...
+```
+
+## Peer Management
+
+### Connection Limits
+
+```yaml
+p2p:
+  max_peers: 50
+  min_peers: 5
+  outbound_peers: 10
+  inbound_peers: 40
+```
+
+### Peer Scoring
+
+Nodes are scored based on:
+- Latency
+- Availability
+- Protocol compliance
+- Block propagation speed
+
+## NAT Traversal
+
+### Supported Methods
+
+| Method | Description |
+|--------|-------------|
+| AutoNAT | Automatic NAT detection |
+| Hole Punching | UDP hole punching |
+| Relay | TURN relay fallback |
+
+### Configuration
+
+```yaml
+p2p:
+  nat:
+    enabled: true
+    method: auto  # auto, hole_punching, relay
+    external_ip: 203.0.113.1
+```
+
+## Troubleshooting
+
+### Check Connectivity
+
+```bash
+aitbc-chain p2p check-connectivity
+```
+
+### List Active Connections
+
+```bash
+aitbc-chain p2p connections
+```
+
+### Debug Mode
+
+```bash
+aitbc-chain start --log-level debug
+```
+
+## Next
+
+- [Quick Start](./1_quick-start.md) — Get started
+- [Configuration](./2_configuration.md) - Configure your node
+- [Operations](./3_operations.md) — Day-to-day ops