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/3_miners/4_earnings.md

@@ -0,0 +1,66 @@
+# Earnings & Payouts
+Track and manage your mining earnings.
+
+## Earnings Overview
+
+```bash
+aitbc miner earnings
+```
+
+Shows:
+- Total earned
+- Pending balance
+- Last payout
+
+## Earnings Breakdown
+
+| Source | Description |
+|--------|-------------|
+| job_completion | Payment for completed jobs |
+| bonus | Performance bonuses |
+| referral | Referral rewards |
+
+## Payout Schedule
+
+| Plan | Schedule | Minimum |
+|------|----------|---------|
+| Automatic | Daily | 10 AITBC |
+| Manual | On request | 1 AITBC |
+
+## Request Payout
+
+```bash
+aitbc wallet withdraw --amount 100 --address <WALLET_ADDRESS>
+```
+
+## Earnings History
+
+```bash
+aitbc miner earnings --history --days 30
+```
+
+## Performance Metrics
+
+```bash
+aitbc miner stats
+```
+
+Shows:
+- Success rate
+- Average completion time
+- Total jobs completed
+- Earnings per GPU/hour
+
+## Tax Reporting
+
+```bash
+aitbc miner earnings --export --year 2026
+```
+
+Export for tax purposes.
+
+## Next
+
+- [Job Management](./3_job-management.md) — Job management
+- [Monitoring](./6_monitoring.md) - Monitor your miner
+- [GPU Setup](./5_gpu-setup.md) — GPU configuration