docs: restructure documentation for improved clarity and navigation

Reorganize documentation into user-focused, developer-focused, and deployment-focused sections.

**New structure:**
- Root: README.md (streamlined), QUICK_START.md, API_REFERENCE.md
- docs/user-guide/: configuration, API usage, integrations, troubleshooting
- docs/developer/: contributing, development setup, testing, architecture
- docs/deployment/: Docker deployment, production checklist, monitoring
- docs/reference/: environment variables, MCP tools, data formats

**Changes:**
- Streamline README.md from 831 to 469 lines
- Create QUICK_START.md for 5-minute onboarding
- Create API_REFERENCE.md as single source of truth for API
- Remove 9 outdated specification docs (v0.2.0 API design)
- Remove DOCKER_API.md (content consolidated into new structure)
- Remove docs/plans/ directory with old design documents
- Update CLAUDE.md with documentation structure guide
- Remove orchestration-specific references

**Benefits:**
- Clear entry points for different audiences
- No content duplication
- Better discoverability through logical hierarchy
- All content reflects current v0.3.0 API

docs/deployment/monitoring.md

@@ -0,0 +1,49 @@
+# Monitoring
+
+Health checks, logging, and metrics.
+
+---
+
+## Health Checks
+
+```bash
+# Manual check
+curl http://localhost:8080/health
+
+# Automated monitoring (cron)
+*/5 * * * * curl -f http://localhost:8080/health || echo "API down" | mail -s "Alert" admin@example.com
+```
+
+---
+
+## Logging
+
+```bash
+# View logs
+docker logs -f ai-trader
+
+# Filter errors
+docker logs ai-trader 2>&1 | grep -i error
+
+# Export logs
+docker logs ai-trader > ai-trader.log 2>&1
+```
+
+---
+
+## Database Monitoring
+
+```bash
+# Database size
+docker exec ai-trader du -h /app/data/jobs.db
+
+# Job statistics
+docker exec ai-trader sqlite3 /app/data/jobs.db \
+  "SELECT status, COUNT(*) FROM jobs GROUP BY status;"
+```
+
+---
+
+## Metrics (Future)
+
+Prometheus metrics planned for v0.4.0.