feat(loyalty): translatable categories + mandatory on earn points

- Add name_translations JSON column to StoreTransactionCategory
  (migration loyalty_008). Stores {"en": "Men", "fr": "Hommes", ...}.
  Model has get_translated_name(lang) helper.
- Admin CRUD form now has FR/DE/LB translation inputs alongside the
  default name.
- Points earn: category_id is now mandatory when the store has
  active categories configured. Returns CATEGORY_REQUIRED error.
- Stamps: category remains optional (quick tap workflow).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/loyalty/schemas/category.py

@@ -10,6 +10,10 @@ class CategoryCreate(BaseModel):
     """Schema for creating a transaction category."""
 
     name: str = Field(..., min_length=1, max_length=100)
+    name_translations: dict[str, str] | None = Field(
+        None,
+        description='Translations keyed by language: {"en": "Men", "fr": "Hommes"}',
+    )
     display_order: int = Field(default=0, ge=0)
 
 
@@ -17,6 +21,7 @@ class CategoryUpdate(BaseModel):
     """Schema for updating a transaction category."""
 
     name: str | None = Field(None, min_length=1, max_length=100)
+    name_translations: dict[str, str] | None = None
     display_order: int | None = Field(None, ge=0)
     is_active: bool | None = None
 
@@ -29,6 +34,7 @@ class CategoryResponse(BaseModel):
     id: int
     store_id: int
     name: str
+    name_translations: dict[str, str] | None = None
     display_order: int
     is_active: bool
     created_at: datetime