Add Share Extension for importing recipes via URL

Adds a Share Extension so users can share URLs from Safari (or any app)
to open the main app with the ImportURLSheet pre-filled. Uses a custom
URL scheme (nextcloud-cookbook://) as the bridge between the extension
and the main app.

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

Nextcloud Cookbook iOS Client/Views/MainView.swift

@@ -20,6 +20,8 @@ struct MainView: View {
 
     @State private var selectedTab: Tab = .recipes
 
+    @Binding var pendingImportURL: String?
+
     enum Tab {
         case recipes, search, mealPlan, groceryList
     }
@@ -106,5 +108,19 @@ struct MainView: View {
             }
             recipeViewModel.presentLoadingIndicator = false
         }
+        .onChange(of: pendingImportURL) { _, newURL in
+            guard let url = newURL, !url.isEmpty else { return }
+            selectedTab = .recipes
+            recipeViewModel.pendingImportURL = url
+            // Dismiss any currently open import sheet before re-presenting
+            if recipeViewModel.showImportURLSheet {
+                recipeViewModel.showImportURLSheet = false
+                DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) {
+                    recipeViewModel.showImportURLSheet = true
+                }
+            } else {
+                recipeViewModel.showImportURLSheet = true
+            }
+        }
     }
 }