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/8_development/6_api-authentication.md

@@ -0,0 +1,85 @@
+---
+title: API Authentication
+description: Understanding and implementing API authentication
+---
+
+# API Authentication
+
+All AITBC API endpoints require authentication using API keys.
+
+## Getting API Keys
+
+### Production
+1. Visit the [AITBC Dashboard](https://dashboard.aitbc.io)
+2. Create an account or sign in
+3. Navigate to API Keys section
+4. Generate a new API key
+
+### Testing/Development
+For integration tests and development, these test keys are available:
+- `${CLIENT_API_KEY}` - For client API access
+- `${MINER_API_KEY}` - For miner registration
+- `test-tenant` - Default tenant ID for testing
+
+## Using API Keys
+
+### HTTP Header
+```http
+X-API-Key: your_api_key_here
+X-Tenant-ID: your_tenant_id  # Optional for multi-tenant
+```
+
+### Environment Variable
+```bash
+export AITBC_API_KEY="your_api_key_here"
+```
+
+### SDK Configuration
+```python
+from aitbc import AITBCClient
+
+client = AITBCClient(api_key="your_api_key")
+```
+
+## Security Best Practices
+
+- Never commit API keys to version control
+- Use environment variables in production
+- Rotate keys regularly
+- Use different keys for different environments
+- Monitor API key usage
+
+## Rate Limits
+
+API requests are rate-limited based on your plan:
+- Free: 60 requests/minute
+- Pro: 600 requests/minute
+- Enterprise: 6000 requests/minute
+
+## Error Handling
+
+```python
+from aitbc.exceptions import AuthenticationError
+
+try:
+    client.jobs.create({...})
+except AuthenticationError:
+    print("Invalid API key")
+```
+
+## Key Management
+
+### View Your Keys
+```bash
+aitbc api-keys list
+```
+
+### Revoke a Key
+```bash
+aitbc api-keys revoke <key_id>
+```
+
+### Regenerate a Key
+```bash
+aitbc api-keys regenerate <key_id>
+```