fix(worker): clear Sonar S5332 hotspot + address review nits

- tests: use https in the OTLP endpoint fixture to clear the S5332
  "http protocol is insecure" security hotspot (quality gate:
  new_security_hotspots_reviewed).
- cli: add the "tracing disabled" else branch in
  _init_worker_observability so the worker logs parity with app.py when no
  OTLP endpoint is set.
- cli: trim the verbose inline comment in worker() (the WHY lives in the
  helper docstring), per review.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_cli.py

@@ -406,14 +406,14 @@ def test_init_worker_observability_sets_up_tracing_when_endpoint(
     """An OTLP endpoint enables tracing so worker spans (parse/embed) export."""
     _init_worker_observability(
         _fake_settings(
-            otel_exporter_otlp_endpoint="http://otel:4317",
+            otel_exporter_otlp_endpoint="https://otel:4317",
             otel_traces_sampler_arg=0.5,
         )
     )
 
     assert patched_observability["tracing"] == {
         "service_name": "nextcloud-mcp-server",
-        "otlp_endpoint": "http://otel:4317",
+        "otlp_endpoint": "https://otel:4317",
         "otlp_verify_ssl": False,
         "sampling_rate": 0.5,
     }