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/repositories/__init__.py

@@ -5,6 +5,7 @@ the contract for data access operations.
 """
 
 from app.domain.repositories.base import Repository
+from app.domain.repositories.comment import CommentRepository
 from app.domain.repositories.post import PostRepository
 
-__all__ = ["Repository", "PostRepository"]
+__all__ = ["Repository", "PostRepository", "CommentRepository"]