feat: add like/unlike toggle on blog posts with per-user tracking

- PostLike domain entity (post_id, liked_by) with BaseEntity integration
- Post entity: add like_count field (default 0) and to_dict serialization
- PostRepository interface: add get_like, add_like, remove_like methods
- TogglePostLikeUseCase: toggle logic (like → unlike, unlike → like)
- PostResponseDTO/PostResponseSchema: add like_count field
- PostLikeORM model with FK to posts and cascade delete
- SQLAlchemyPostRepository: implement like query/add/remove with ORM mapping
- DI provider registration for TogglePostLikeUseCase
- API endpoint POST /api/v1/posts/{id}/like (auth required)
- Unit tests: PostLike entity, Post.like_count, TogglePostLikeUseCase (7 tests)
- API tests: POST /api/v1/posts/{id}/like (4 tests)
- Test model files: FEATURE_LIKES.md, TEST_MODEL.md updated

app/application/use_cases/toggle_like.py

@@ -0,0 +1,102 @@
+"""Toggle post like use case.
+
+This module implements the use case for toggling likes on blog posts.
+If the user already liked the post, the like is removed (unlike).
+If not, a new like is added.
+"""
+
+from uuid import UUID
+
+from app.application.dtos.post import PostResponseDTO
+from app.application.interfaces import TransactionManager
+from app.domain.entities import Post
+from app.domain.entities.like import PostLike
+from app.domain.exceptions import NotFoundException
+from app.domain.repositories import PostRepository
+
+
+class TogglePostLikeUseCase:
+    """Use case for toggling a like on a blog post.
+
+    Handles like/unlike toggle logic. If the user or device has already
+    liked the post, the like is removed. Otherwise, a new like is created.
+
+    Attributes:
+        _post_repo: Repository for post and like data access.
+        _tx_manager: Transaction manager for commit control.
+
+    Example:
+        >>> use_case = TogglePostLikeUseCase(post_repo, tx_manager)
+        >>> result = await use_case.execute("my-post-slug", "user-123")
+    """
+
+    def __init__(
+        self,
+        post_repo: PostRepository,
+        tx_manager: TransactionManager,
+    ) -> None:
+        """Initialize use case with dependencies.
+
+        Args:
+            post_repo: Repository for post and like operations.
+            tx_manager: Transaction manager instance.
+        """
+        self._post_repo = post_repo
+        self._tx_manager = tx_manager
+
+    async def execute(self, post_id: UUID, liked_by: str) -> PostResponseDTO:
+        """Toggle like on a post.
+
+        If the user/device already liked the post, remove the like.
+        Otherwise, add a new like.
+
+        Args:
+            post_id: UUID of the post to toggle like on.
+            liked_by: User ID or device identifier.
+
+        Returns:
+            PostResponseDTO with updated like_count.
+
+        Raises:
+            NotFoundException: If post with given ID does not exist.
+        """
+        post = await self._post_repo.get_by_id(post_id)
+        if not post:
+            raise NotFoundException(f"Post with id '{post_id}' not found")
+
+        existing_like = await self._post_repo.get_like(post_id, liked_by)
+
+        if existing_like:
+            await self._post_repo.remove_like(post_id, liked_by)
+            post.like_count = max(0, post.like_count - 1)
+        else:
+            new_like = PostLike(post_id=post_id, liked_by=liked_by)
+            await self._post_repo.add_like(new_like)
+            post.like_count += 1
+
+        await self._post_repo.update(post)
+        await self._tx_manager.commit()
+
+        return self._map_to_dto(post)
+
+    def _map_to_dto(self, post: Post) -> PostResponseDTO:
+        """Map domain entity to response DTO.
+
+        Args:
+            post: Domain post entity.
+
+        Returns:
+            PostResponseDTO with all post attributes including like_count.
+        """
+        return PostResponseDTO(
+            id=post.id,
+            title=post.title.value,
+            content=post.content.value,
+            slug=post.slug.value,
+            author_id=post.author_id,
+            published=post.published,
+            like_count=post.like_count,
+            tags=post.tags.copy(),
+            created_at=post.created_at,
+            updated_at=post.updated_at,
+        )