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/api/v1/__init__.py

@@ -6,7 +6,9 @@ all v1 endpoint routers.
 
 from fastapi import APIRouter
 
+from app.presentation.api.v1.comments import router as comments_router
 from app.presentation.api.v1.posts import router as posts_router
 
 router = APIRouter(prefix="/v1")
 router.include_router(posts_router)
+router.include_router(comments_router)