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/domain/entities/comment_like.py

@@ -0,0 +1,40 @@
+"""Domain entity for CommentLike.
+
+This module defines the CommentLike entity that tracks which users
+have liked which comments.
+"""
+
+from dataclasses import dataclass
+from typing import Any
+from uuid import UUID
+
+from app.domain.entities.base import BaseEntity
+
+
+@dataclass(kw_only=True)
+class CommentLike(BaseEntity):
+    """Comment like domain entity.
+
+    Tracks a like on a comment by a user. Each like is uniquely
+    identified by its entity ID.
+
+    Attributes:
+        comment_id: UUID of the liked comment.
+        liked_by: Identifier of the user who liked.
+    """
+
+    comment_id: UUID
+    liked_by: str
+
+    def to_dict(self) -> dict[str, Any]:
+        """Convert entity to dictionary.
+
+        Returns:
+            Dictionary with all CommentLike attributes.
+        """
+        return {
+            "id": str(self.id),
+            "comment_id": str(self.comment_id),
+            "liked_by": self.liked_by,
+            "created_at": self.created_at.isoformat(),
+        }