feat(web): add PostHog events for user creation and Ask GitHub login wall

- Add `wa_user_created` event fired on successful user sign-up
- Add `wa_askgh_login_wall_prompted` event fired when an unauthenticated
  user attempts to ask a question on Ask GitHub and is shown the login modal
- Add debug logging to server-side PostHog event capture

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: msukkari

packages/web/src/app/[domain]/askgh/[owner]/[repo]/components/landingPage.tsx

@@ -14,6 +14,7 @@ import type { IdentityProviderMetadata } from "@/lib/identityProviders";
 import { Descendant, Transforms } from "slate";
 import { useSlate } from "slate-react";
 import { useCallback, useEffect, useMemo, useState, useRef } from "react";
+import { captureEvent } from "@/hooks/useCaptureEvent";
 
 const PENDING_MESSAGE_KEY = "askgh_pending_message";
 
@@ -55,6 +56,7 @@ export const LandingPage = ({
     // Intercept submit to check auth status
     const handleSubmit = useCallback((children: Descendant[]) => {
         if (!isAuthenticated) {
+            captureEvent('wa_askgh_login_wall_prompted', {});
             // Store message in sessionStorage to survive OAuth redirect
             sessionStorage.setItem(PENDING_MESSAGE_KEY, JSON.stringify(children));
             setIsLoginModalOpen(true);

packages/web/src/lib/posthogEvents.ts

@@ -231,6 +231,8 @@ export type PosthogEventMap = {
         userId: string,
     },
     //////////////////////////////////////////////////////////////////
+    wa_askgh_login_wall_prompted: {},
+    //////////////////////////////////////////////////////////////////
     wa_demo_docs_link_pressed: {},
     wa_demo_search_example_card_pressed: {
         exampleTitle: string,