Fix category handling, recipe management, and dark mode toggle tint

- Map uncategorized category between * (internal) and empty string
  (API) so selecting Sonstige/Other correctly persists to the server
- Default new recipes to Other (*) category and remove None option
- Add "New Category" option to category picker in recipe edit view
- Include newly created/imported recipes in recently viewed list and
  pre-fetch thumbnails so images display immediately
- Remove deleted recipes from recently viewed list
- Remove broad .tint(.primary) from RecipeTabView that caused white
  toggles in Settings during dark mode
- Rename German "Other" translation from Andere to Sonstige
- Add missing translations for Servings stepper and new category strings

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

Nextcloud Cookbook iOS Client/Data/ObservableRecipeDetail.swift

@@ -45,7 +45,7 @@ class ObservableRecipeDetail: ObservableObject {
         description = ""
         url = ""
         recipeYield = 1
-        recipeCategory = ""
+        recipeCategory = "*"
         tool = []
         recipeIngredient = []
         recipeInstructions = []
@@ -67,7 +67,7 @@ class ObservableRecipeDetail: ObservableObject {
         description = recipeDetail.description
         url = recipeDetail.url ?? ""
         recipeYield = recipeDetail.recipeYield == 0 ? 1 : recipeDetail.recipeYield // Recipe yield should not be zero
-        recipeCategory = recipeDetail.recipeCategory
+        recipeCategory = recipeDetail.recipeCategory.isEmpty ? "*" : recipeDetail.recipeCategory
         tool = recipeDetail.tool
         recipeIngredient = recipeDetail.recipeIngredient
         recipeInstructions = recipeDetail.recipeInstructions
@@ -92,7 +92,7 @@ class ObservableRecipeDetail: ObservableObject {
             description: self.description,
             url: self.url,
             recipeYield: self.recipeYield,
-            recipeCategory: self.recipeCategory,
+            recipeCategory: self.recipeCategory == "*" ? "" : self.recipeCategory,
             tool: self.tool,
             recipeIngredient: self.recipeIngredient,
             recipeInstructions: self.recipeInstructions,