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

sentry.server.config.ts

@@ -0,0 +1,44 @@
+import * as Sentry from '@sentry/nextjs';
+
+const SENTRY_DSN = process.env.SENTRY_DSN || '';
+
+if (SENTRY_DSN) {
+  Sentry.init({
+    dsn: SENTRY_DSN,
+    environment: process.env.NODE_ENV || 'development',
+    enabled: process.env.NODE_ENV !== 'development',
+
+    tracesSampleRate: 1.0,
+
+    beforeSend(event, hint) {
+      const error = hint.originalException;
+
+      if (error instanceof Error) {
+        event.contexts = {
+          ...event.contexts,
+          runtime: {
+            name: 'node',
+            version: process.version,
+          },
+          application: {
+            name: 'novalon-website',
+            version: process.env.npm_package_version || 'unknown',
+          },
+        };
+      }
+
+      if (event.request?.cookies) {
+        delete event.request.cookies['session_id'];
+        delete event.request.cookies['token'];
+      }
+
+      return event;
+    },
+  });
+
+  console.log('[Sentry] Server-side monitoring initialized');
+} else {
+  console.warn('[Sentry] SENTRY_DSN not configured, server-side error monitoring disabled');
+}
+
+export default Sentry;