feat: downgrade tech stack to stable versions and integrate GA4 error monitoring

- Downgrade Next.js 16→14.2, React 19→18.3, Tailwind 4→3.4
- Add comprehensive GA4 error monitoring system
- Create Jenkins CI/CD pipeline with quality gates
- Fix build issues: ESLint, SWC conflict, config format
- Add documentation for deployment and error tracking

src/components/analytics/CookieConsent.tsx

@@ -48,6 +48,7 @@ export function CookieConsent() {
           necessary: true,
           analytics: legacyConsent === 'granted',
           marketing: false,
+          functionality: true,
           timestamp: Date.now(),
         };
         storePreferences(migratedPrefs);
@@ -91,6 +92,7 @@ export function CookieConsent() {
       necessary: true,
       analytics: true,
       marketing: false,
+      functionality: true,
       timestamp: Date.now(),
     };
     handleSavePreferences(allAccepted);
@@ -102,6 +104,7 @@ export function CookieConsent() {
       necessary: true,
       analytics: false,
       marketing: false,
+      functionality: true,
       timestamp: Date.now(),
     };
     handleSavePreferences(allRejected);

src/components/analytics/GlobalErrorTracker.tsx

@@ -0,0 +1,81 @@
+'use client';
+
+import { useEffect } from 'react';
+import { trackError } from '@/lib/analytics';
+
+const IGNORED_ERRORS = [
+  /_AutofillCallbackHandler/,
+  /ResizeObserver loop limit exceeded/,
+  /webkit\.messageHandlers/,
+  /Non-Error promise rejection captured/,
+  /^Loading CSS chunk.*failed$/,
+  /^Loading chunk.*failed$/,
+  /^Failed to fetch dynamically imported module/,
+  /Script error/,
+  /NetworkError/,
+];
+
+function shouldIgnoreError(message: string): boolean {
+  return IGNORED_ERRORS.some((pattern) => pattern.test(message));
+}
+
+export function GlobalErrorTracker() {
+  useEffect(() => {
+    if (typeof window === 'undefined') return;
+
+    const handleGlobalError = (
+      event: ErrorEvent
+    ) => {
+      if (shouldIgnoreError(event.message)) return;
+
+      trackError(
+        'javascript_error',
+        event.message,
+        false,
+        {
+          filename: event.filename || '',
+          lineno: event.lineno || 0,
+          colno: event.colno || 0,
+          stack: event.error?.stack?.slice(0, 500) || '',
+        }
+      );
+    };
+
+    const handleUnhandledRejection = (event: PromiseRejectionEvent) => {
+      const message =
+        event.reason?.message || String(event.reason) || 'Unknown promise rejection';
+
+      if (shouldIgnoreError(message)) return;
+
+      trackError(
+        'unhandled_promise_rejection',
+        message,
+        false,
+        {
+          reason_type: event.reason?.constructor?.name || 'Unknown',
+          stack: event.reason?.stack?.slice(0, 500) || '',
+        }
+      );
+    };
+
+    const handleResourceError = () => {
+      trackError('resource_loading_error', 'Failed to load resource', false);
+    };
+
+    window.addEventListener('error', handleGlobalError, true);
+    window.addEventListener('unhandledrejection', handleUnhandledRejection);
+    document.addEventListener('error', handleResourceError, true);
+
+    if (process.env.NODE_ENV === 'development') {
+      console.log('[GA4] Global error tracker initialized');
+    }
+
+    return () => {
+      window.removeEventListener('error', handleGlobalError, true);
+      window.removeEventListener('unhandledrejection', handleUnhandledRejection);
+      document.removeEventListener('error', handleResourceError, true);
+    };
+  }, []);
+
+  return null;
+}