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/9_upgrades.md

@@ -0,0 +1,77 @@
+# Node Upgrades
+Guide for upgrading your blockchain node.
+
+## Upgrade Process
+
+### Check Current Version
+
+```bash
+aitbc-chain version
+```
+
+### Check for Updates
+
+```bash
+aitbc-chain check-update
+```
+
+### Upgrade Steps
+
+```bash
+# 1. Backup data
+aitbc-chain backup --output /backup/chain-$(date +%Y%m%d).tar.gz
+
+# 2. Stop node gracefully
+aitbc-chain stop
+
+# 3. Upgrade software
+pip install --upgrade aitbc-chain
+
+# 4. Review migration notes
+cat CHANGELOG.md
+
+# 5. Start node
+aitbc-chain start
+```
+
+## Version-Specific Upgrades
+
+### v0.1.0 → v0.2.0
+
+```bash
+# Database migration required
+aitbc-chain migrate --from v0.1.0
+```
+
+### v0.2.0 → v0.3.0
+
+```bash
+# Configuration changes
+aitbc-chain migrate-config --from v0.2.0
+```
+
+## Rollback Procedure
+
+```bash
+# If issues occur, rollback
+pip install aitbc-chain==0.1.0
+
+# Restore from backup
+aitbc-chain restore --input /backup/chain-YYYYMMDD.tar.gz
+
+# Start old version
+aitbc-chain start
+```
+
+## Upgrade Notifications
+
+```bash
+# Enable upgrade alerts
+aitbc-chain alert --metric upgrade_available --action notify
+```
+
+## Next
+
+- [Quick Start](./1_quick-start.md) — Get started
+- [Operations](./3_operations.md) — Day-to-day ops
+- [Monitoring](./7_monitoring.md) — Monitoring