fix: resolve review blockers for comments redesign

- Fix context key mismatch in _render_htmx_success ('reply' vs 'comment')
- Update OOB swap selector to match new sibling relationship for replies container
- Update HTMX reply tests to verify correct OOB selector and content rendering
- Fix variable naming in _reply.html to match parent context

apps/comments/views.py

@@ -148,10 +148,14 @@ class CommentCreateView(View):
         if comment.is_approved:
             ctx = _comment_template_context(comment, article, request)
             if comment.parent_id:
-                comment_html = render_to_string("comments/_reply.html", ctx, request)
+                # _reply.html expects 'reply' context key
+                reply_ctx = ctx.copy()
+                reply_ctx["reply"] = reply_ctx.pop("comment")
+                comment_html = render_to_string("comments/_reply.html", reply_ctx, request)
+                # .replies-container is now a sibling of #comment-{id}
                 oob_html = (
                     f'<div hx-swap-oob="beforeend:#comment-{comment.parent_id} '
-                    f'.replies-container">{comment_html}</div>'
+                    f'~ .replies-container">{comment_html}</div>'
                 )
             else:
                 comment_html = render_to_string("comments/_comment.html", ctx, request)