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/__init__.py

@@ -12,6 +12,7 @@ from app.application.use_cases import (
     GetPostUseCase,
     ListPostsUseCase,
     PublishPostUseCase,
+    TogglePostLikeUseCase,
     UpdatePostUseCase,
 )
 
@@ -26,4 +27,5 @@ __all__ = [
     "DeletePostUseCase",
     "ListPostsUseCase",
     "PublishPostUseCase",
+    "TogglePostLikeUseCase",
 ]