refactor: simplify OpenTelemetry tracing configuration

Simplifies the OpenTelemetry tracing setup by removing the redundant
OTEL_ENABLED flag and using the presence of OTEL_EXPORTER_OTLP_ENDPOINT
to determine if tracing should be enabled. This follows the standard
OpenTelemetry environment variable conventions more closely.

Changes:
- Remove OTEL_ENABLED/tracing_enabled flag in favor of checking if
  OTEL_EXPORTER_OTLP_ENDPOINT is set
- Add OTEL_EXPORTER_VERIFY_SSL configuration option for OTLP endpoints
  with self-signed certificates (defaults to false for development)
- Move HTTPXClientInstrumentor initialization to module level to ensure
  httpx calls are traced across all Nextcloud API requests
- Add tracing spans to vector sync operations (scan_user_documents)
- Fix authorization header logging to only warn about missing headers
  in OAuth mode (BasicAuth mode doesn't use Authorization headers)
- Update observability documentation to reflect simplified configuration
- Refactor Dockerfile to use --no-editable flag for uv sync

Breaking changes:
- OTEL_ENABLED environment variable is removed
- Tracing is now automatically enabled when OTEL_EXPORTER_OTLP_ENDPOINT
  is set

Migration guide:
- Remove OTEL_ENABLED=true from environment configuration
- Tracing will be enabled automatically if OTEL_EXPORTER_OTLP_ENDPOINT
  is configured

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

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

docker-compose.yml

@@ -98,16 +98,20 @@ services:
       #- QDRANT_URL=http://qdrant:6333  # Uncomment for network mode
       #- QDRANT_API_KEY=${QDRANT_API_KEY:-my_secret_api_key}  # Only for network mode
 
+      # Observability
+      #- OTEL_SERVICE_NAME=nextcloud-mcp-docker-compose
+      #- OTEL_EXPORTER_OTLP_ENDPOINT=http://otel-collector:4317
+
       # Collection naming: Auto-generated as {deployment-id}-{model-name}
       # - Deployment ID: OTEL_SERVICE_NAME (if set) or hostname (fallback)
       # - Model name: OLLAMA_EMBEDDING_MODEL
       # - Example: "nextcloud-mcp-server-nomic-embed-text"
       # - Changing models creates new collection (requires re-embedding)
       # - Set QDRANT_COLLECTION to override auto-generation:
-      - QDRANT_COLLECTION=nextcloud_content
+      #- QDRANT_COLLECTION=nextcloud_content
 
       # Ollama configuration (optional - uses SimpleEmbeddingProvider if not set)
-      # - OLLAMA_BASE_URL=https://ollama.internal.coutinho.io:443
+      # - OLLAMA_BASE_URL=http://ollama:11434
       # - OLLAMA_EMBEDDING_MODEL=nomic-embed-text  # Changing this creates new collection
       # - OLLAMA_VERIFY_SSL=false