refactor(usage): address round-1 review on PR #871

- store: add optional `enabled` param to record_usage_event so hot-path
  callers (nc_semantic_search) pass the already-resolved flag instead of
  forcing a second uncached Settings build (ADR-024); falls back to
  get_settings() when None so the store stays self-gating for standalone
  use.
- hooks: thread enabled= through both call sites; bump the outer
  shared()/construction failure log from debug → warning so "metering
  enabled but no billing data" is visible at the default INFO level.
- migration: instantiate postgresql.JSONB() to match the sibling
  TIMESTAMP(timezone=True) column.
- tests: fix the misleading "asyncpg returns JSONB as a JSON string"
  comment; add occurred_at dialect round-trip test and an enabled-param
  short-circuit test.

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

nextcloud_mcp_server/server/semantic.py

@@ -534,9 +534,16 @@ def configure_semantic_tools(mcp: FastMCP):
                             "fusion": fusion,
                             "doc_types": doc_types,
                         },
+                        # Pass the already-resolved flag so the store doesn't
+                        # rebuild Settings on this hot query path (ADR-024).
+                        enabled=settings.usage_metering_enabled,
                     )
                 except Exception:
-                    logger.debug(
+                    # Reached only when shared()/store construction itself
+                    # raises (record_usage_event swallows its own write
+                    # failures). Metering is on, so warn — a silent DEBUG line
+                    # would hide "operator enabled metering but gets no data".
+                    logger.warning(
                         "usage metering hook (embeddings_queries) skipped",
                         exc_info=True,
                     )