fix(hub): chat scroll-to-bottom, message loading on group switch, connecting spinner

Three regressions fixed in ChatPanel:

- Scroll pinning: layout effect now depends on [messages, hasMore] so the
  "load older" button appearance triggers a re-pin; setHasMore is called
  before setMessages to avoid an intermediate render without the button;
  fit() is wrapped in fitAndPin() so panel resizing re-pins the scroll.

- Message loading on group switch: fetch effect depends on the status prop
  instead of transportRef.current?.connected to avoid racing with
  GroupPage's cleanup; loadedRef resets on fetch failure so a retry works.

- Connecting spinner restored in the Chat tab empty state.

Adds structural regression tests (test_chat_scroll_bottom.py) that lock
the dependency arrays and setState ordering so these invariants break
loudly in CI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions