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/presentation/schemas/__init__.py

@@ -4,6 +4,11 @@ This module re-exports all Pydantic schemas used for
 request/response validation in the API layer.
 """
 
+from app.presentation.schemas.comment import (
+    CommentCreateSchema,
+    CommentLikeResponseSchema,
+    CommentResponseSchema,
+)
 from app.presentation.schemas.post import (
     PostBaseSchema,
     PostCreateSchema,
@@ -22,4 +27,7 @@ __all__ = [
     "PostListResponseSchema",
     "PostSearchSchema",
     "PostPublishSchema",
+    "CommentCreateSchema",
+    "CommentResponseSchema",
+    "CommentLikeResponseSchema",
 ]