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/models/transaction_category.py

@@ -15,6 +15,7 @@ from sqlalchemy import (
     String,
     UniqueConstraint,
 )
+from sqlalchemy.dialects.sqlite import JSON
 from sqlalchemy.orm import relationship
 
 from app.core.database import Base
@@ -29,6 +30,11 @@ class StoreTransactionCategory(Base, TimestampMixin):
     id = Column(Integer, primary_key=True, index=True)
     store_id = Column(Integer, ForeignKey("stores.id"), nullable=False)
     name = Column(String(100), nullable=False)
+    name_translations = Column(
+        JSON,
+        nullable=True,
+        comment='Language-keyed name dict, e.g. {"en": "Men", "fr": "Hommes"}',
+    )
     display_order = Column(Integer, nullable=False, default=0)
     is_active = Column(Boolean, nullable=False, default=True)
 
@@ -42,3 +48,9 @@ class StoreTransactionCategory(Base, TimestampMixin):
 
     def __repr__(self):
         return f"<StoreTransactionCategory(id={self.id}, store={self.store_id}, name='{self.name}')>"
+
+    def get_translated_name(self, lang: str) -> str:
+        """Get name in the given language, falling back to self.name."""
+        if self.name_translations and isinstance(self.name_translations, dict):
+            return self.name_translations.get(lang) or self.name
+        return self.name