reviews: ask unico a premium existentes, funnel instrumentado y fix source unknown del paywall

- requestForExistingPremiumUser(): prompt nativo una sola vez para quien
  ya era premium antes del ask post-compra (evento review_prompt_premium_user)
- Funnel de semanas completadas emite review_funnel_shown/positive/negative/dismissed
- Paywall de Home via sheet(item:) con PaywallPresentation: el source viaja
  con la presentacion; antes dos @State separados hacian que a veces se
  registrara paywall_viewed con source=unknown (post_onboarding nunca llegaba)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013H6bXqGX1ygwib1Dm3n3UG

MealMood/Services/ReviewPromptService.swift

@@ -8,6 +8,7 @@ final class ReviewPromptService {
     private let reviewCompletedKey = "review_funnel_completed"
     private let lastPromptedCompletedWeeksKey = "review_funnel_last_prompted_completed_weeks"
     private let postPurchaseAskedKey = "review_post_purchase_asked"
+    private let premiumUserAskedKey = "review_premium_user_asked"
     private let minimumCompletedWeeksToStart = 1
     private let promptIntervalWeeks = 2
 
@@ -22,6 +23,7 @@ final class ReviewPromptService {
     /// user just paid, so sentiment is at its peak. Once per user; the small
     /// delay lets the "premium active" state render before the system alert.
     func requestAfterPurchase() {
+        guard !hasCompletedReviewFlow else { return }
         guard !UserDefaults.standard.bool(forKey: postPurchaseAskedKey) else { return }
         UserDefaults.standard.set(true, forKey: postPurchaseAskedKey)
         AnalyticsService.logEvent("review_prompt_post_purchase")
@@ -32,6 +34,21 @@ final class ReviewPromptService {
         }
     }
 
+    /// One-time ask for users who were already premium before the post-purchase
+    /// prompt existed — they never went through it, and a paying user is the
+    /// most likely 5-star reviewer the app has.
+    func requestForExistingPremiumUser() {
+        guard !hasCompletedReviewFlow else { return }
+        guard !UserDefaults.standard.bool(forKey: premiumUserAskedKey) else { return }
+        UserDefaults.standard.set(true, forKey: premiumUserAskedKey)
+        AnalyticsService.logEvent("review_prompt_premium_user")
+        Task { @MainActor in
+            try? await Task.sleep(for: .seconds(2))
+            requestReview()
+            markReviewCompleted()
+        }
+    }
+
     func shouldShowFunnelAfterWeekCompletion(completedWeeks: Int) -> Bool {
         guard !hasCompletedReviewFlow else { return false }
         guard completedWeeks >= minimumCompletedWeeksToStart else { return false }