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>

nextcloud_mcp_server/observability/readiness.py

@@ -38,8 +38,9 @@ class ReadinessCache(BaseModel):
     """Time-bounded snapshot of external dependency health.
 
     Written only by the background refresh loop and read only by the readiness
-    handler. No locking: assignment into ``statuses`` is atomic under the GIL,
-    and a reader tolerates seeing the previous value for one entry.
+    handler. The single-writer invariant (one refresh loop) is what makes this
+    safe without a lock; a reader simply tolerates seeing the previous value for
+    one entry until the next refresh.
     """
 
     ttl_seconds: float = 30.0