Implement application-wide PostHog user identification

[coderabbitai]

Description

PostHog user identification is not implemented consistently across the application. Currently, user identification only occurs in specific authentication flows (email/password signup), while other parts of the application do not identify users at all.

Current State

Limited identification in email/password flows only:

In apps/web/app/(auth)/sign-up/page.tsx and apps/web/app/(auth)/sign-in/page.tsx:

// Only happens for email/password auth
posthog.identify(data.email, {
  email: data.email,
  name: data.name,
});

Missing identification in:

• Google OAuth sign-up/sign-in flows
• Application routes after authentication
• User session restoration on page reload
• Profile updates or user data changes

Expected Behavior

PostHog should identify authenticated users consistently across the entire application:

• After any authentication method (email/password, Google OAuth, etc.)
• When the application loads and a session exists
• When user data changes (profile updates)
• Throughout the user journey regardless of entry point

Proposed Solution

Implement a centralized user identification strategy:

1. Client-side approach: Add a useEffect in a root layout component (e.g., app/layout.tsx) that:

   • Checks authentication state on mount
   • Calls posthog.identify() when a user session is detected
   • Re-identifies on authentication state changes

2. Server-side approach: Implement user identification in middleware or a root server component that:

   • Runs after authentication is confirmed
   • Ensures identification happens before rendering

3. Event-driven approach: Listen for authentication events and trigger identification automatically

Impact

Without proper user identification:

• User analytics are incomplete and inaccurate
• Cannot track user journeys across sessions
• Event attribution to users is missing
• Product analytics and funnel analysis are unreliable

References

• Related PR: feat: added posthog integration #7
• Discussion: feat: added posthog integration #7 (comment)
• Reported by: @eswaldots