Add Web Vitals performance tracking (LCP, INP, CLS, FCP, TTFB)

End-to-end performance metrics tracking: dedicated database table with
percentile aggregation, tracker collection behind data-perf attribute,
/api/send handling, report API endpoints, and Performance dashboard page
with threshold-based metric cards, time-series chart, and per-page breakdown.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/queries/sql/index.ts

@@ -22,6 +22,8 @@ export * from './getWeeklyTraffic';
 export * from './pageviews/getPageviewExpandedMetrics';
 export * from './pageviews/getPageviewMetrics';
 export * from './pageviews/getPageviewStats';
+export * from './performance/getPerformanceStats';
+export * from './performance/savePerformance';
 export * from './reports/getBreakdown';
 export * from './reports/getFunnel';
 export * from './reports/getJourney';