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/iosMain/kotlin/com/tt/honeyDue/analytics/PostHogAnalytics.ios.kt

@@ -18,6 +18,10 @@ actual object PostHogAnalytics {
         // iOS uses Swift PostHogAnalytics.shared.capture() directly
     }
 
+    actual fun captureException(throwable: Throwable, properties: Map<String, Any>?) {
+        // iOS exception capture is done in Swift via AnalyticsManager
+    }
+
     actual fun screen(screenName: String, properties: Map<String, Any>?) {
         // iOS uses Swift PostHogAnalytics.shared.screen() directly
     }
@@ -29,4 +33,8 @@ actual object PostHogAnalytics {
     actual fun flush() {
         // iOS uses Swift PostHogAnalytics.shared.flush() directly
     }
+
+    actual fun setupExceptionHandler() {
+        // iOS exception handler is set up in Swift via AnalyticsManager.setupExceptionHandler()
+    }
 }