Avoid reusing category thumbnail images in all recipes preview mosaic

Track which recipe IDs are used as category thumbnails and prefer
different images for the all recipes 2x2 mosaic, falling back to
category thumbnails only when not enough other images are available.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Nextcloud Cookbook iOS Client/AppState.swift

@@ -17,6 +17,7 @@ import UIKit
     @Published var recipeDetails: [Int: RecipeDetail] = [:]
     @Published var timers: [String: RecipeTimer] = [:]
     @Published var categoryImages: [String: UIImage] = [:]
+    @Published var categoryImageRecipeIds: Set<Int> = []
     @Published var recentRecipes: [Recipe] = []
     @Published var categoryAccessDates: [String: Date] = [:]
     @Published var manualCategoryOrder: [String] = []
@@ -320,6 +321,7 @@ import UIKit
         for recipe in recipes {
             if let image = await getImage(id: recipe.recipe_id, size: .THUMB, fetchMode: .preferLocal) {
                 self.categoryImages[categoryName] = image
+                self.categoryImageRecipeIds.insert(recipe.recipe_id)
                 return
             }
         }

Nextcloud Cookbook iOS Client/Views/Recipes/AllRecipesCategoryCardView.swift

@@ -72,15 +72,29 @@ struct AllRecipesCategoryCardView: View {
         allRecipes.shuffle()
 
         // Filter to recipes that have an image URL, then pick 4
+        // Prefer recipes not already used as category thumbnails
+        let categoryImageIds = appState.categoryImageRecipeIds
         var candidates: [Recipe] = []
+        var fallbackCandidates: [Recipe] = []
         var seenIds: Set<Int> = []
         for recipe in allRecipes {
             guard let url = recipe.imageUrl, !url.isEmpty else { continue }
             guard !seenIds.contains(recipe.recipe_id) else { continue }
             seenIds.insert(recipe.recipe_id)
-            candidates.append(recipe)
+            if categoryImageIds.contains(recipe.recipe_id) {
+                fallbackCandidates.append(recipe)
+            } else {
+                candidates.append(recipe)
+            }
             if candidates.count >= 4 { break }
         }
+        // Fill remaining slots from fallback if needed
+        if candidates.count < 4 {
+            for recipe in fallbackCandidates {
+                candidates.append(recipe)
+                if candidates.count >= 4 { break }
+            }
+        }
 
         var images: [UIImage] = []
         for recipe in candidates {