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/8_troubleshooting.md

@@ -0,0 +1,153 @@
+# Troubleshooting
+Common issues and solutions for blockchain nodes.
+
+## Common Issues
+
+### Node Won't Start
+
+```bash
+# Check logs
+tail -f ~/.aitbc/logs/chain.log
+
+# Common causes:
+# - Port already in use
+# - Corrupted database
+# - Invalid configuration
+```
+
+**Solutions:**
+```bash
+# Kill existing process
+sudo lsof -i :8080
+sudo kill $(sudo lsof -t -i :8080)
+
+# Reset database
+rm -rf ~/.aitbc/data/chain.db
+aitbc-chain init
+
+# Validate config
+aitbc-chain validate-config
+```
+
+### Sync Stuck
+
+```bash
+# Check sync status
+aitbc-chain sync-status
+
+# Force sync from scratch
+aitbc-chain reset --hard
+
+# Check peer connectivity
+aitbc-chain p2p connections
+```
+
+**Solutions:**
+```bash
+# Add more peers
+aitbc-chain p2p add-bootstrap /dns4/new-peer.example.com/tcp/7070/p2p/...
+
+# Clear peer database
+rm -rf ~/.aitbc/data/peers.db
+
+# Restart with fresh sync
+aitbc-chain start --sync-mode full
+```
+
+### P2P Connection Issues
+
+```bash
+# Check connectivity
+aitbc-chain p2p check-connectivity
+
+# Test port forwarding
+curl http://localhost:8080/rpc/net_info
+```
+
+**Solutions:**
+```bash
+# Open firewall
+sudo ufw allow 7070/tcp
+sudo ufw allow 8080/tcp
+
+# Check NAT configuration
+aitbc-chain p2p nat-status
+
+# Use relay mode
+aitbc-chain start --p2p-relay-enabled
+```
+
+### High Memory Usage
+
+```bash
+# Check memory usage
+htop | grep aitbc-chain
+
+# Check database size
+du -sh ~/.aitbc/data/
+```
+
+**Solutions:**
+```bash
+# Prune old data
+aitbc-chain prune --keep-blocks 10000
+
+# Reduce peer count
+# Edit config: max_peers: 25
+
+# Enable compression
+aitbc-chain start --db-compression
+```
+
+### RPC Not Responding
+
+```bash
+# Check RPC status
+curl http://localhost:8080/rpc/health
+
+# Check if RPC is enabled
+aitbc-chain status | grep RPC
+```
+
+**Solutions:**
+```bash
+# Restart with RPC enabled
+aitbc-chain start --rpc-enabled
+
+# Check CORS settings
+# Edit config: rpc.cors_origins
+
+# Increase rate limits
+# Edit config: rpc.rate_limit: 2000
+```
+
+## Diagnostic Commands
+
+```bash
+# Full system check
+aitbc-chain doctor
+
+# Network diagnostics
+aitbc-chain diagnose network
+
+# Database diagnostics
+aitbc-chain diagnose database
+
+# Log analysis
+aitbc-chain logs --analyze
+```
+
+## Getting Help
+
+```bash
+# Generate debug report
+aitbc-chain debug-report > debug.txt
+
+# Share on Discord or GitHub Issues
+```
+
+## Next
+
+- [Quick Start](./1_quick-start.md) — Get started
+- [Configuration](./2_configuration.md) - Configure your node
+- [Operations](./3_operations.md) — Day-to-day ops