Add PostHog exception capture for crash reporting

Android: uncaught exception handler sends $exception events with stack
trace to PostHog, flushes before delegating to default handler.
iOS: NSSetUncaughtExceptionHandler captures crashes via PostHogSDK,
avoids @MainActor deadlock by calling SDK directly.
Common: captureException() available for non-fatal catches app-wide.
Platform stubs for jvm/js/wasmJs.

composeApp/src/androidMain/kotlin/com/tt/honeyDue/MainActivity.kt

@@ -80,6 +80,9 @@ class MainActivity : FragmentActivity(), SingletonImageLoader.Factory {
         // Initialize PostHog Analytics
         PostHogAnalytics.initialize(application, debug = true) // Set debug=false for release
 
+        // Install uncaught exception handler to capture crashes to PostHog
+        PostHogAnalytics.setupExceptionHandler()
+
         // Handle deep link, notification navigation, and file import from intent
         handleDeepLink(intent)
         handleNotificationNavigation(intent)