feat(observability): Add comprehensive monitoring with Prometheus and OpenTelemetry

- Add Prometheus metrics for HTTP, MCP tools, Nextcloud API, OAuth, vector sync, and DB operations
- Add OpenTelemetry distributed tracing with OTLP export
- Add structured JSON logging with trace context correlation
- Add ObservabilityMiddleware for automatic HTTP instrumentation
- Add app_name attribute to all client classes for per-app metrics
- Add configuration for metrics, tracing, and logging via environment variables
- Add documentation in docs/observability.md
- Fix graceful degradation when tracing is disabled (default state)
- Fix uvicorn logging configuration to use observability formatters

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

docker-compose.yml

@@ -88,11 +88,13 @@ services:
       - VECTOR_SYNC_SCAN_INTERVAL=10
       - VECTOR_SYNC_PROCESSOR_WORKERS=1
 
+      - LOG_FORMAT=json
+
       # Qdrant configuration (three modes):
       # 1. Network mode: Set QDRANT_URL=http://qdrant:6333 (requires qdrant service)
       # 2. In-memory mode: Set QDRANT_LOCATION=:memory: (default if nothing set)
       # 3. Persistent local: Set QDRANT_LOCATION=/app/data/qdrant (stored in mcp-data volume)
-      - QDRANT_LOCATION=:memory:
+      - QDRANT_LOCATION=/app/data/qdrant
       # - QDRANT_URL=http://qdrant:6333  # Uncomment for network mode
       # - QDRANT_API_KEY=${QDRANT_API_KEY:-my_secret_api_key}  # Only for network mode
       - QDRANT_COLLECTION=nextcloud_content