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.

iosApp/iosApp/Analytics/AnalyticsManager.swift

@@ -91,6 +91,47 @@ final class AnalyticsManager {
         PostHogSDK.shared.capture("screen_viewed", properties: props)
     }
 
+    // MARK: - Exception / Crash Capture
+
+    /// Capture a Swift Error as a PostHog `$exception` event.
+    func captureException(_ error: Error, properties: [String: Any]? = nil) {
+        guard isConfigured else { return }
+        var props: [String: Any] = [
+            "$exception_type": String(describing: type(of: error)),
+            "$exception_message": error.localizedDescription,
+            "$exception_stack_trace_raw": Thread.callStackSymbols.joined(separator: "\n")
+        ]
+        if let properties { props.merge(properties) { _, new in new } }
+        PostHogSDK.shared.capture("$exception", properties: props)
+    }
+
+    /// Capture an NSException as a PostHog `$exception` event.
+    func captureNSException(_ exception: NSException, isFatal: Bool = false) {
+        guard isConfigured else { return }
+        PostHogSDK.shared.capture("$exception", properties: [
+            "$exception_type": exception.name.rawValue,
+            "$exception_message": exception.reason ?? "No reason",
+            "$exception_stack_trace_raw": exception.callStackSymbols.joined(separator: "\n"),
+            "$exception_is_fatal": isFatal
+        ])
+    }
+
+    /// Install an uncaught NSException handler that captures crashes to PostHog
+    /// before the app terminates. Call this once after configure().
+    func setupExceptionHandler() {
+        NSSetUncaughtExceptionHandler { exception in
+            // Cannot use AnalyticsManager.shared here (may deadlock on @MainActor),
+            // so call PostHogSDK directly.
+            PostHogSDK.shared.capture("$exception", properties: [
+                "$exception_type": exception.name.rawValue,
+                "$exception_message": exception.reason ?? "No reason",
+                "$exception_stack_trace_raw": exception.callStackSymbols.joined(separator: "\n"),
+                "$exception_is_fatal": true
+            ])
+            PostHogSDK.shared.flush()
+        }
+    }
+
     // MARK: - Flush & Reset
 
     func flush() {

iosApp/iosApp/iOSApp.swift

@@ -55,6 +55,9 @@ struct iOSApp: App {
         if !UITestRuntime.isEnabled {
             // Initialize PostHog Analytics (must use Swift AnalyticsManager, not the Kotlin stub)
             AnalyticsManager.shared.configure()
+
+            // Install uncaught exception handler to capture crashes to PostHog
+            AnalyticsManager.shared.setupExceptionHandler()
         }
     }