Feature/rest for grocery list

[JonathanPschl]

Closes #52

REST API for Grocery Lists

Adds a full CRUD REST API for persisted grocery lists in grocery-service, backed by grocery-db, exposed through the api-gateway and documented via OpenAPI/Swagger.

What's included

Endpoints (/api/grocery-list)

Method	Path	Description
GET	/history	20 most recent grocery lists (summaries), newest first
GET	/history/{id}	Single grocery list with its items
POST	/history	Create a grocery list with items → 201 Created + Location
DELETE	/history/{id}	Delete a grocery list and its items → 204 No Content

Implementation

• Controller / Service / Repository layering: GroceryListController, GroceryListService, GroceryListRepository.
• Entities: GroceryList, GroceryItem, GroceryCategory (JPA, mapped to the existing grocery-db schema).
• DTOs: request/response records (GroceryListCreateRequest, GroceryItemRequestDTO, GroceryListDetailDTO, GroceryListSummaryDTO, GroceryItemResponseDTO) — entities are never exposed directly.
• Validation: name and userId required (400 otherwise); unknown category → 400; missing list → 404.

OpenAPI / Swagger

• Added springdoc-openapi and OpenApiConfig (title, version, bearerAuth JWT scheme).
• Endpoints annotated with @Operation / @ApiResponse.
• Aggregated in the gateway's Swagger UI (/v3/api-docs/grocery-service).

Database & gateway

• grocery-db/init.sql: grocery_category enum type.
• user-db/init.sql: seeded dev admin (admin@bytebite.dev / password).
• api-gateway: routes /api/grocery-list/** to grocery-service.

[timn21]

lgtm