Replace PostHog integration with AnalyticsManager architecture

Remove old PostHogAnalytics singleton and replace with guide-based
two-file architecture: AnalyticsManager (singleton wrapper with super
properties, session replay, opt-out, subscription funnel) and
AnalyticsEvent (type-safe enum with associated values).

Key changes:
- New API key, self-hosted analytics endpoint
- All 19 events ported to type-safe AnalyticsEvent enum
- Screen tracking via AnalyticsManager.Screen enum + SwiftUI modifier
- Remove all identify() calls — fully anonymous analytics
- Add lifecycle hooks: flush on background, update super properties on foreground
- Add privacy opt-out toggle in Settings
- Subscription funnel methods ready for IAP integration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

iosApp/iosApp/Helpers/WidgetActionProcessor.swift

@@ -71,7 +71,7 @@ final class WidgetActionProcessor {
                 WidgetDataManager.shared.clearPendingState(forTaskId: taskId)
                 // Refresh tasks to update UI
                 await refreshTasks()
-            } else if let error = result as? ApiResultError {
+            } else if let error = ApiResultBridge.error(from: result) {
                 print("WidgetActionProcessor: Failed to complete task \(taskId): \(error.message)")
                 // Remove action to avoid infinite retries
                 WidgetDataManager.shared.removeAction(action)