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>

nextcloud_mcp_server/observability/__init__.py

@@ -0,0 +1,35 @@
+"""
+Observability module for the Nextcloud MCP Server.
+
+This module provides:
+- Prometheus metrics collection
+- OpenTelemetry distributed tracing
+- Enhanced structured logging with trace correlation
+- Monitoring middleware for Starlette/FastAPI
+
+Usage:
+    from nextcloud_mcp_server.observability import setup_observability
+
+    # In app.py lifespan
+    setup_observability(app, config)
+"""
+
+from nextcloud_mcp_server.observability.logging_config import (
+    get_uvicorn_logging_config,
+    setup_logging,
+)
+from nextcloud_mcp_server.observability.metrics import (
+    get_metrics_handler,
+    setup_metrics,
+)
+from nextcloud_mcp_server.observability.middleware import ObservabilityMiddleware
+from nextcloud_mcp_server.observability.tracing import setup_tracing
+
+__all__ = [
+    "setup_logging",
+    "get_uvicorn_logging_config",
+    "setup_metrics",
+    "setup_tracing",
+    "get_metrics_handler",
+    "ObservabilityMiddleware",
+]