fix(config): correct OIDC token-type/scopes env keys; address review round 1

- _DEFAULTS keys for NEXTCLOUD_OIDC_TOKEN_TYPE / NEXTCLOUD_OIDC_SCOPES were
  registered as oidc_* (uppercasing to OIDC_*), so dynaconf
  (ignore_unknown_envvars) never read the NEXTCLOUD_-prefixed env vars and the
  fields stayed at their defaults. Prefix the keys to match _field_map; add a
  regression test.
- Add gte=1 validator for HEALTH_READY_REFRESH_INTERVAL and a 1..65535 range
  validator for PORT.
- Tie ReadinessCache.ttl_seconds to 2x the configured refresh interval so
  is_stale() stays meaningful when the interval is tuned.
- Raise the refresh-loop exception log from DEBUG to WARNING.
- Make health_ready a sync handler (no awaits); dedupe the localhost fallback
  into _DEFAULT_MCP_SERVER_URL; use pytest.approx for the float default.

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

tests/unit/test_readiness_cache.py

@@ -18,7 +18,7 @@ def test_dependency_status_defaults():
     status = DependencyStatus(name="nextcloud")
     assert status.healthy is None  # not yet checked
     assert status.detail == "pending"
-    assert status.checked_at == 0.0
+    assert status.checked_at == pytest.approx(0.0)
 
 
 def test_update_and_snapshot_round_trip():