Add PostHog analytics — full event tracking across all pages

Tracks pageviews, hero/CTA clicks, product teaser clicks, app card
and detail views, newsletter signups, nav interactions, and footer
link clicks with structured properties for PostHog dashboards.

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

components/ui/NewsletterForm.tsx

@@ -1,8 +1,9 @@
 'use client'
 
 import { useState } from 'react'
+import { posthog } from '@/lib/posthog'
 
-export default function NewsletterForm() {
+export default function NewsletterForm({ source = 'homepage' }: { source?: string }) {
   const [email, setEmail] = useState('')
   const [submitted, setSubmitted] = useState(false)
 
@@ -21,7 +22,10 @@ export default function NewsletterForm() {
     <form
       onSubmit={(e) => {
         e.preventDefault()
-        if (email.trim()) setSubmitted(true)
+        if (email.trim()) {
+        posthog.capture('newsletter_signup', { source })
+        setSubmitted(true)
+      }
       }}
       style={{ display: 'flex', gap: 12, maxWidth: 480, margin: '0 auto', flexWrap: 'wrap' }}
     >