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/domain/entities/post.py

@@ -44,6 +44,7 @@ class Post(BaseEntity):
     slug: Slug
     author_id: str
     published: bool = False
+    like_count: int = 0
     tags: list[str] = field(default_factory=list)
 
     def publish(self) -> None:
@@ -114,6 +115,7 @@ class Post(BaseEntity):
             "slug": self.slug.value,
             "author_id": self.author_id,
             "published": self.published,
+            "like_count": self.like_count,
             "tags": self.tags.copy(),
             "created_at": self.created_at.isoformat(),
             "updated_at": self.updated_at.isoformat(),