refactor: remove performance insights (Web Vitals) feature entirely

Remove Performance tab, PerformanceStats component, settings toggle,
Web Vitals observers from tracking script, and all related API types
and SWR hooks. Duration tracking is preserved.

public/script.js

@@ -32,59 +32,15 @@
   const ttlHours = storageMode === 'local' ? parseFloat(script.getAttribute('data-storage-ttl') || '24') : 0;
   const ttlMs = ttlHours > 0 ? ttlHours * 60 * 60 * 1000 : 0;
 
-  // * Performance Monitoring (Core Web Vitals) State
   let currentEventId = null;
-  let metrics = { lcp: 0, cls: 0, inp: 0 };
-  let lcpObserved = false;
-  let clsObserved = false;
-  let performanceInsightsEnabled = false;
 
   // * Time-on-page tracking: records when the current pageview started
   var pageStartTime = 0;
 
-  // * Minimal Web Vitals Observer
-  function observeMetrics() {
-    try {
-      if (typeof PerformanceObserver === 'undefined') return;
-
-      // * LCP (Largest Contentful Paint) - fires when the browser has determined the LCP element (often 2–4s+ after load)
-      new PerformanceObserver((entryList) => {
-        const entries = entryList.getEntries();
-        const lastEntry = entries[entries.length - 1];
-        if (lastEntry) {
-          metrics.lcp = lastEntry.startTime;
-          lcpObserved = true;
-        }
-      }).observe({ type: 'largest-contentful-paint', buffered: true });
-
-      // * CLS (Cumulative Layout Shift) - accumulates when elements shift after load
-      new PerformanceObserver((entryList) => {
-        for (const entry of entryList.getEntries()) {
-          if (!entry.hadRecentInput) {
-            metrics.cls += entry.value;
-            clsObserved = true;
-          }
-        }
-      }).observe({ type: 'layout-shift', buffered: true });
-
-      // * INP (Interaction to Next Paint) - Simplified (track max duration)
-      new PerformanceObserver((entryList) => {
-        const entries = entryList.getEntries();
-        for (const entry of entries) {
-           // * Track longest interaction
-           if (entry.duration > metrics.inp) metrics.inp = entry.duration;
-        }
-      }).observe({ type: 'event', buffered: true, durationThreshold: 16 });
-
-    } catch (e) {
-      // * Browser doesn't support PerformanceObserver or specific entry types
-    }
-  }
-
   function sendMetrics() {
     if (!currentEventId) return;
 
-    // * Calculate time-on-page in seconds (always sent, even without performance insights)
+    // * Calculate time-on-page in seconds
     var durationSec = pageStartTime > 0 ? Math.round((Date.now() - pageStartTime) / 1000) : 0;
 
     var payload = { event_id: currentEventId };
@@ -92,17 +48,8 @@
     // * Always include duration if we have a valid measurement
     if (durationSec > 0) payload.duration = durationSec;
 
-    // * Only include Web Vitals when performance insights are enabled
-    if (performanceInsightsEnabled) {
-      // * Only include metrics the browser actually reported. Sending 0 would either be
-      // * rejected by the backend (LCP/INP must be > 0) or skew averages.
-      if (lcpObserved && metrics.lcp > 0) payload.lcp = metrics.lcp;
-      if (clsObserved) payload.cls = metrics.cls;
-      if (metrics.inp > 0) payload.inp = metrics.inp;
-    }
-
-    // * Skip if nothing to send (no duration and no vitals)
-    if (!payload.duration && !performanceInsightsEnabled) return;
+    // * Skip if nothing to send (no duration)
+    if (!payload.duration) return;
 
     var data = JSON.stringify(payload);
 
@@ -118,14 +65,10 @@
     }
   }
 
-  // * Start observing metrics immediately (buffered observers will capture early metrics)
-  // * Metrics will only be sent if performance insights are enabled (checked in sendMetrics)
-  observeMetrics();
-
   // * Send metrics when user leaves or hides the page
   document.addEventListener('visibilitychange', () => {
     if (document.visibilityState === 'hidden') {
-      // * Delay metrics slightly so in-flight LCP/CLS callbacks can run before we send
+      // * Delay slightly so duration measurement captures final moment
       setTimeout(sendMetrics, 150);
     }
   });
@@ -306,9 +249,6 @@
 
   // * Track pageview
   function trackPageview() {
-    var routeChangeTime = performance.now();
-    var isSpaNav = !!currentEventId;
-
     const path = cleanPath();
 
     // * Skip if same path was just tracked (refresh dedup)
@@ -321,9 +261,6 @@
         sendMetrics();
     }
 
-    metrics = { lcp: 0, cls: 0, inp: 0 };
-    lcpObserved = false;
-    clsObserved = false;
     currentEventId = null;
     pageStartTime = 0;
     // * Only send external referrer on the first pageview (landing page).
@@ -375,21 +312,6 @@
       if (data && data.id) {
         currentEventId = data.id;
         pageStartTime = Date.now();
-        // * For SPA navigations the browser never emits a new largest-contentful-paint
-        // * (LCP is only for full document loads). After the new view has had time to
-        // * paint, we record time-from-route-change as an LCP proxy so /products etc.
-        // * get a value. If the user navigates away before the delay, we leave LCP unset.
-        if (isSpaNav) {
-          var thatId = data.id;
-          // * Run soon so we set lcpObserved before the user leaves; 500ms was too long
-          // * and we often sent metrics (next nav or visibilitychange+150ms) before it ran.
-          setTimeout(function() {
-            if (!lcpObserved && currentEventId === thatId) {
-              metrics.lcp = Math.round(performance.now() - routeChangeTime);
-              lcpObserved = true;
-            }
-          }, 100);
-        }
       }
     }).catch(() => {
       // * Silently fail - don't interrupt user experience