feat: integrate PostHog analytics for frontend and PWA

- Install posthog-js and @posthog/react packages
- Add PostHogProvider wrapper in main.tsx for both apps
- Configure PostHog with EU instance and 2026-01-30 defaults
- Add environment variables for API key and host
- Update docker-compose.coolify.yml with PostHog build args

frontend/src/main.tsx

@@ -2,6 +2,7 @@ import { StrictMode } from 'react'
 import ReactDOM from 'react-dom/client'
 import { RouterProvider } from '@tanstack/react-router'
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { PostHogProvider } from '@posthog/react'
 import { router } from './routes'
 import { AuthProvider } from './contexts/AuthContext'
 import { initializeTheme } from './lib/theme'
@@ -11,12 +12,22 @@ initializeTheme();
 
 const queryClient = new QueryClient()
 
+const posthogOptions = {
+  api_host: import.meta.env.VITE_PUBLIC_POSTHOG_HOST,
+  defaults: '2026-01-30',
+} as const
+
 ReactDOM.createRoot(document.getElementById('root')!).render(
   <StrictMode>
-    <QueryClientProvider client={queryClient}>
-      <AuthProvider>
-        <RouterProvider router={router} />
-      </AuthProvider>
-    </QueryClientProvider>
+    <PostHogProvider 
+      apiKey={import.meta.env.VITE_PUBLIC_POSTHOG_KEY} 
+      options={posthogOptions}
+    >
+      <QueryClientProvider client={queryClient}>
+        <AuthProvider>
+          <RouterProvider router={router} />
+        </AuthProvider>
+      </QueryClientProvider>
+    </PostHogProvider>
   </StrictMode>,
 )