[BE-09] Build RestaurantModule with CRUD endpoints - entity exists, module does not

[Leothosine]

Problem

src/modules/restaurant/restaurant.entity.ts defines the Restaurant entity but there is no RestaurantModule, RestaurantService, or RestaurantController. Restaurants can only be created as a side effect of user registration. There is no API to update restaurant info, change the URL slug, manage settings JSON, or support multi-location scenarios.

Proposed Solution

Create a complete RestaurantModule with the following endpoints, all scoped to the authenticated user's restaurantId from their JWT payload:

Method	Path	Description
GET	/api/restaurant	Get own restaurant info
PATCH	/api/restaurant	Update name, phone, email, WhatsApp
GET	/api/restaurant/settings	Get settings JSON blob
PATCH	/api/restaurant/settings	Merge-update settings JSON

Acceptance Criteria

• Authenticated admin can fetch their own restaurant with GET /api/restaurant
• PATCH /api/restaurant with a slug already used by another restaurant returns 409
• Cross-restaurant data access returns 403 (restaurantId comes from JWT, not request body)
• Slug validation rejects non-URL-safe characters (regex: /^[a-z0-9-]+$/)
• Settings endpoint stores and returns arbitrary JSON without overwriting unrelated keys