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/PostHogProvider.tsx

@@ -0,0 +1,21 @@
+'use client'
+
+import { useEffect } from 'react'
+import { usePathname } from 'next/navigation'
+import { initPostHog, posthog } from '@/lib/posthog'
+
+export default function PostHogProvider({ children }: { children: React.ReactNode }) {
+  useEffect(() => {
+    initPostHog()
+  }, [])
+
+  const pathname = usePathname()
+
+  useEffect(() => {
+    if (posthog.__loaded) {
+      posthog.capture('$pageview', { $current_url: window.location.href })
+    }
+  }, [pathname])
+
+  return <>{children}</>
+}