feat: add comments feature with nested replies and recursive rendering

Implement full comments system: domain entities (Comment, CommentLike),
value objects (CommentContent), use cases (CRUD, like toggle), SQLAlchemy
repository, API v1 endpoints, web UI with comment form and nested replies,
i18n translations (EN/RU/FR/DE), and E2E tests.

Fix nested reply (reply-to-reply) not displaying — the flat reply_comments
dict was only queried for top-level comment IDs, so deeply nested replies
were saved to DB (incrementing comment count) but never rendered. Switch
to a recursive Jinja2 macro that renders any nesting depth.

app/application/use_cases/list_comments.py

@@ -0,0 +1,63 @@
+"""List comments use case.
+
+This module implements the use case for listing comments on a blog post.
+"""
+
+from uuid import UUID
+
+from app.application.dtos.comment import CommentResponseDTO
+from app.domain.entities.comment import Comment
+from app.domain.repositories import CommentRepository
+
+
+class ListCommentsUseCase:
+    """Use case for listing comments on a blog post.
+
+    Retrieves all comments for a given post ordered by creation time.
+
+    Attributes:
+        _comment_repo: Repository for comment data access.
+    """
+
+    def __init__(
+        self,
+        comment_repo: CommentRepository,
+    ) -> None:
+        """Initialize use case with dependencies.
+
+        Args:
+            comment_repo: Repository for comment operations.
+        """
+        self._comment_repo = comment_repo
+
+    async def execute(self, post_id: UUID) -> list[CommentResponseDTO]:
+        """List all comments for a post.
+
+        Args:
+            post_id: UUID of the post.
+
+        Returns:
+            List of CommentResponseDTO for the post.
+        """
+        comments = await self._comment_repo.get_by_post(post_id)
+        return [self._map_to_dto(c) for c in comments]
+
+    def _map_to_dto(self, comment: Comment) -> CommentResponseDTO:
+        """Map domain entity to response DTO.
+
+        Args:
+            comment: Domain Comment entity.
+
+        Returns:
+            CommentResponseDTO with all comment attributes.
+        """
+        return CommentResponseDTO(
+            id=comment.id,
+            post_id=comment.post_id,
+            author_id=comment.author_id,
+            content=comment.content.value,
+            parent_id=comment.parent_id,
+            like_count=comment.like_count,
+            created_at=comment.created_at,
+            updated_at=comment.updated_at,
+        )