Feature/shopping list UI

[timn21]

Shopping List & Recipes UI + per-user REST alignment

Adds the Recipes and Grocery Lists frontend, a full Recipes REST subsystem, and reworks
the existing grocery-list API.

Client

• Recipes view (RecipeListView, new) — accordion of saved recipes, ingredients
  lazy-loaded on expand, copy & delete, loading/error/empty states.
• Grocery Lists view (GroceryListView, new) — accordion with progress bar and
  per-item "picked up" checkboxes (persisted), copy & delete; collapsed cards show
  progress from summary counts, items load lazily on expand.
• App.tsx — both views wired to the backend (load summaries, lazy detail, optimistic
  per-item PATCH toggle, delete); a generated dish is persisted as both a recipe and a
  grocery list.

Recipes: New REST subsystem (grocery-service)

• Recipe entity + RecipeRepository, RecipeService, RecipeController.
• GET/POST/PUT/DELETE /api/recipes (+ /{recipeId}), per-user via X-User-Id,
  summary-list + lazy detail. New DTOs (RecipeCreateRequest, RecipeDetailDTO,
  RecipeItemRequest/ResponseDTO, RecipeSummaryDTO).

Grocery-list: Reworked to match

• Paths: /api/grocery-list/history → /api/grocery-list, /history/{id} →
  /{groceryListId}.
• Identity: userId in the request body → X-User-Id header (set by the gateway);
  all operations are now per-user (ownership-scoped, 404 on not-owned) and return all of
  the caller's lists instead of the global top-20.
• New endpoints: PUT /{groceryListId} (replace) and
  PATCH /{groceryListId}/items/{itemId} (toggle a single item's purchased).
• Summaries now include itemCount/purchasedCount (single aggregate query) so the
  collapsed cards show progress without loading items; summary id field id →
  groceryListId.
• Quantity is nullable (Double); category parsing falls back to OTHER instead
  of throwing on unknown values.
• Shared GroceryItem table for both subsystems via GroceryItemMapper + ItemRequest
  (validates name, normalizes unit, shared parseCategory); recipe/grocery
  controllers/services/DTOs aligned in structure.

Kubernetes

• Helm: grocery-db/user-db added to Kubernetes deployment

[JonathanPschl]

Looks good! One thing to change maybe: I think we agreed that the GroceryLists will be generated by selecting Recipes from the RecipeList. Currently we immediately push a generated Recipe also as a GroceryList. I think we should have a quick call and discuss if we remove this until we implement #55 or if we merge it now and immediately finish and ship #55 asap.

This PR should also note that it closes:
#13
#15
#24
#53