feat(observability): add sentry monitoring

sentry.server.config.ts

@@ -0,0 +1,23 @@
+// This file configures the initialization of Sentry on the server.
+// The config you add here will be used whenever the server handles a request.
+// https://docs.sentry.io/platforms/javascript/guides/nextjs/
+
+import * as Sentry from "@sentry/nextjs";
+
+const dsn = process.env.SENTRY_DSN ?? process.env.NEXT_PUBLIC_SENTRY_DSN;
+
+if (dsn) {
+  Sentry.init({
+    dsn,
+
+    tracesSampleRate: Number(
+      process.env.SENTRY_TRACES_SAMPLE_RATE ??
+        (process.env.NODE_ENV === "production" ? "0.1" : "1"),
+    ),
+
+    enableLogs: true,
+
+    // Chat content and auth data are sensitive; do not send default PII.
+    sendDefaultPii: false,
+  });
+}