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.

tests/unit/domain/test_comment_like_entity.py

@@ -0,0 +1,50 @@
+"""Tests for CommentLike domain entity.
+
+This module tests the CommentLike entity creation, attributes,
+and BaseEntity integration.
+"""
+
+from uuid import UUID
+
+from app.domain.entities.comment_like import CommentLike
+
+
+class TestCommentLikeEntity:
+    """Tests for the CommentLike domain entity.
+
+    Covers TC-UNIT-831.
+    """
+
+    def test_comment_like_creation(self) -> None:
+        """Test creating a CommentLike with valid attributes.
+
+        TC-UNIT-831: Positive — create CommentLike instance.
+
+        Expected:
+            - comment_id matches input
+            - liked_by matches input
+            - id is a valid UUID
+            - created_at is set
+        """
+        comment_id = UUID("00000000-0000-0000-0000-000000000001")
+        liked_by = "user-123"
+
+        like = CommentLike(comment_id=comment_id, liked_by=liked_by)
+
+        assert like.comment_id == comment_id
+        assert like.liked_by == liked_by
+        assert isinstance(like.id, UUID)
+        assert like.created_at is not None
+
+    def test_comment_like_to_dict(self) -> None:
+        """Test CommentLike to_dict serialization."""
+        comment_id = UUID("00000000-0000-0000-0000-000000000001")
+        liked_by = "device-abc-123"
+
+        like = CommentLike(comment_id=comment_id, liked_by=liked_by)
+        data = like.to_dict()
+
+        assert data["comment_id"] == str(comment_id)
+        assert data["liked_by"] == liked_by
+        assert "id" in data
+        assert "created_at" in data