feat: Add API endpoint for managing categories

app/services/category_service.py

@@ -0,0 +1,26 @@
+from typing import List
+from sqlalchemy.ext.asyncio import AsyncSession
+from app.repositories.category_repository import CategoryRepository
+from app.db.models.category import Category
+from app.core.exceptions import CategoryAlreadyExistsException
+
+
+class CategoryService:
+    def __init__(self, db: AsyncSession):
+        self.db = db
+        self.repo = CategoryRepository(db)
+
+    async def list_categories(self) -> List[Category]:
+        """Returns all categories alphabetical list"""
+        return await self.repo.list_all()
+
+    async def create_category(self, name: str) -> Category:
+        """Creates a new category, validating uniqueness first"""
+        name_clean = name.strip()
+        existing = await self.repo.get_by_name(name_clean)
+        if existing:
+            raise CategoryAlreadyExistsException(name_clean)
+
+        category = await self.repo.create(name_clean)
+        await self.db.commit()
+        return category