fix(#355 review round-2 F9-F11): register-gate test + shutdown idle-close + DB-path metrics gate

- F10 [stability]: closeMetricsServer() now calls server.closeIdleConnections()
  + server.unref() after server.close(). server.close()'s callback doesn't fire
  until keep-alive sockets drain, and the scraper (VictoriaMetrics/vmagent) holds
  an idle keep-alive socket — so onModuleDestroy's awaited close would hang until
  the scraper disconnects or the orchestrator SIGKILLs on the kill-grace window.
  closeIdleConnections() drops idle keep-alive sockets so shutdown completes
  immediately (Node 22, per the Dockerfile base).
- F9 [test]: client-telemetry.module.spec.ts pins the E1=B register() gate — the
  core of the "public endpoint OFF by default" decision: flag unset / any non-
  "true" value ("false"/""/"0"/…) → empty controllers+providers (route absent);
  "true"/"TRUE" → registers VitalsController + VitalsService. A flag-inversion or
  truthiness regression that reopened the anonymous disk-fill surface now fails.
- F11 [regression/perf]: the db_query_duration_seconds token work (firstSqlToken
  regex + Set lookup) is now gated on isMetricsEnabled() in database.module.ts, so
  a non-metrics deployment pays NOTHING per query (previously observeDbQuery
  no-op'd but the token was still computed on every query). Also hoisted the
  13-element known-token Set to a module const (KNOWN_SQL_TOKENS) so it's built
  once, not per query.

Gate: server tsc 0; metrics + vitals + client-telemetry suites pass (incl. the
new register-gate test).

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

apps/server/src/database/database.module.ts

@@ -40,7 +40,10 @@ import { PageListener } from '@docmost/db/listeners/page.listener';
 import { PostgresJSDialect } from 'kysely-postgres-js';
 import * as postgres from 'postgres';
 import { normalizePostgresUrl } from '../common/helpers';
-import { observeDbQuery } from '../integrations/metrics/metrics.registry';
+import {
+  observeDbQuery,
+  isMetricsEnabled,
+} from '../integrations/metrics/metrics.registry';
 import { firstSqlToken } from '../integrations/metrics/metrics.constants';
 
 @Global()
@@ -70,12 +73,16 @@ import { firstSqlToken } from '../integrations/metrics/metrics.constants';
         plugins: [new CamelCasePlugin()],
         log: (event: LogEvent) => {
           // #355 — db_query_duration_seconds, labelled by the leading SQL token
-          // (bounded cardinality). No-op when METRICS_PORT is unset. Runs for
-          // every query, independent of the dev-only debug logging below.
-          observeDbQuery(
-            firstSqlToken(event.query.sql),
-            event.queryDurationMillis / 1000,
-          );
+          // (bounded cardinality). Gated on isMetricsEnabled() so the token work
+          // (regex + Set lookup) is skipped entirely when metrics are OFF — not
+          // just observeDbQuery no-op'd — so a non-metrics deployment pays nothing
+          // per query. Runs independent of the dev-only debug logging below.
+          if (isMetricsEnabled()) {
+            observeDbQuery(
+              firstSqlToken(event.query.sql),
+              event.queryDurationMillis / 1000,
+            );
+          }
 
           if (environmentService.getNodeEnv() !== 'development') return;
           const logger = new Logger(DatabaseModule.name);