feat: Enhance PostHog integration with referral tracking and error handling

- Added referral code tracking in PostHog initialization to capture initial and last seen referral codes.
- Wrapped PostHog capture calls in a safeCapture function to prevent app breakage due to ad-blockers.
- Introduced PostHogReferral component in PostHogProvider for improved referral tracking.

surfsense_web/components/providers/PostHogProvider.tsx

@@ -5,17 +5,17 @@ import posthog from "posthog-js";
 import type { ReactNode } from "react";
 import "../../instrumentation-client";
 import { PostHogIdentify } from "./PostHogIdentify";
+import { PostHogReferral } from "./PostHogReferral";
 
 interface PostHogProviderProps {
 	children: ReactNode;
 }
 
 export function PostHogProvider({ children }: PostHogProviderProps) {
-	// posthog-js is initialized by importing instrumentation-client.ts above
-	// We wrap the app with the PostHogProvider for hook access
 	return (
 		<PHProvider client={posthog}>
 			<PostHogIdentify />
+			<PostHogReferral />
 			{children}
 		</PHProvider>
 	);

surfsense_web/components/providers/PostHogReferral.tsx

@@ -0,0 +1,34 @@
+"use client";
+
+import { useEffect } from "react";
+import { trackReferralLanding } from "@/lib/posthog/events";
+
+const REF_STORAGE_KEY = "surfsense_ref_code";
+
+/**
+ * Captures the ?ref=<code> URL parameter on first landing and fires a
+ * PostHog event so marketing campaigns can be attributed.
+ *
+ * The ref code is persisted to sessionStorage so it survives client-side
+ * navigations that strip query params (e.g. login redirect), but a fresh
+ * event is fired for each new browser session with a ref param.
+ */
+export function PostHogReferral() {
+	useEffect(() => {
+		if (typeof window === "undefined") return;
+
+		const params = new URLSearchParams(window.location.search);
+		const ref = params.get("ref");
+
+		if (ref) {
+			try {
+				sessionStorage.setItem(REF_STORAGE_KEY, ref);
+			} catch {
+				// Private browsing may block sessionStorage
+			}
+			trackReferralLanding(ref, window.location.href);
+		}
+	}, []);
+
+	return null;
+}