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/5_validator.md

@@ -0,0 +1,95 @@
+# Validator Operations
+Guide for running a validator node in the AITBC network.
+
+## Becoming a Validator
+
+### Requirements
+
+| Requirement | Value |
+|-------------|-------|
+| Stake | 1000 AITBC |
+| Node uptime | 99%+ |
+| Technical capability | Must run node 24/7 |
+| Geographic distribution | One per region preferred |
+
+### Registration
+
+```bash
+aitbc-chain validator register --stake 1000
+```
+
+### Activate Validator Status
+
+```bash
+aitbc-chain validator activate
+```
+
+## Validator Duties
+
+### Block Production
+
+Validators take turns producing blocks:
+- Round-robin selection
+- Fixed 2-second block time
+- Missed blocks result in reduced rewards
+
+### Transaction Validation
+
+- Verify transaction signatures
+- Check sender balance
+- Validate smart contract execution
+
+### Network Participation
+
+- Maintain P2P connections
+- Propagate blocks to peers
+- Participate in consensus votes
+
+## Validator Rewards
+
+### Block Rewards
+
+| Block Position | Reward |
+|----------------|--------|
+| Proposer | 1 AITBC |
+| Validator (any) | 0.1 AITBC |
+
+### Performance Bonuses
+
+- 100% uptime: 1.5x multiplier
+- 99-100% uptime: 1.2x multiplier
+- <99% uptime: 1.0x multiplier
+
+## Validator Monitoring
+
+```bash
+# Check validator status
+aitbc-chain validator status
+
+# View performance metrics
+aitbc-chain validator metrics
+
+# Check missed blocks
+aitbc-chain validator missed-blocks
+```
+
+## Validator Slashing
+
+### Slashing Conditions
+
+| Violation | Penalty |
+|-----------|---------|
+| Double signing | 5% stake |
+| Extended downtime | 1% stake |
+| Invalid block | 2% stake |
+
+### Recovery
+
+- Partial slashing can be recovered
+- Full slashing requires re-registration
+
+## Next
+
+- [Quick Start](./1_quick-start.md) — Get started
+- [Consensus](./4_consensus.md) — Consensus mechanism
+- [Monitoring](./7_monitoring.md) — Monitoring