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/7_api-miner.md

@@ -0,0 +1,141 @@
+# Miner API Reference
+Complete API reference for miner operations.
+
+## Endpoints
+
+### Register Miner
+
+```
+POST /v1/miners
+```
+
+**Request Body:**
+
+```json
+{
+  "name": "my-miner",
+  "gpu_type": "v100",
+  "gpu_count": 1,
+  "location": "us-east",
+  "price_per_hour": 0.05,
+  "max_concurrent": 4
+}
+```
+
+**Response:**
+
+```json
+{
+  "miner_id": "miner_xyz789",
+  "api_key": "key_abc123",
+  "status": "pending"
+}
+```
+
+### Update Miner
+
+```
+PUT /v1/miners/{miner_id}
+```
+
+### Heartbeat
+
+```
+POST /v1/miners/{miner_id}/heartbeat
+```
+
+**Response:**
+
+```json
+{
+  "status": "ok",
+  "jobs_assigned": 0,
+  "queue_length": 5
+}
+```
+
+### List Available Jobs
+
+```
+GET /v1/miners/{miner_id}/jobs/available
+```
+
+**Response:**
+
+```json
+{
+  "jobs": [
+    {
+      "job_id": "job_abc123",
+      "model": "gpt2",
+      "gpu_type": "v100",
+      "gpu_count": 1,
+      "estimated_time": 600,
+      "price": 0.05
+    }
+  ]
+}
+```
+
+### Accept Job
+
+```
+POST /v1/miners/{miner_id}/jobs/{job_id}/accept
+```
+
+### Complete Job
+
+```
+POST /v1/miners/{miner_id}/jobs/{job_id}/complete
+```
+
+**Request Body:**
+
+```json
+{
+  "result_hash": "sha256:abc123...",
+  "metrics": {
+    "execution_time_seconds": 600,
+    "gpu_time_seconds": 600
+  }
+}
+```
+
+### Get Miner Stats
+
+```
+GET /v1/miners/{miner_id}/stats
+```
+
+**Response:**
+
+```json
+{
+  "total_jobs": 100,
+  "success_rate": 0.98,
+  "average_completion_time": 600,
+  "earnings": 50.5,
+  "earnings_per_gpu_hour": 0.05
+}
+```
+
+## Error Codes
+
+| Code | Description |
+|------|-------------|
+| 400 | Invalid request |
+| 401 | Unauthorized |
+| 404 | Miner/job not found |
+| 409 | Job already assigned |
+| 422 | Validation error |
+
+## Rate Limits
+
+- 60 requests/minute
+- 10 job operations/minute
+
+## Next
+
+- [Quick Start](./1_quick-start.md) — Get started
+- [Job Management](./3_job-management.md) — Job management
+- [Monitoring](./6_monitoring.md) - Monitor your miner