ui: show sender names in group bubbles with stable colors

docs/core-checklist-status.md

@@ -14,7 +14,7 @@ Legend:
 5. Chat List - `DONE` (all/pinned/archive/sort/unread)
 6. Chat Types - `DONE` (private/group/channel)
 7. Chat Creation - `DONE` (private/group/channel)
-8. Messages (base) - `DONE` (send/read/edit/delete/delete for all)
+8. Messages (base) - `DONE` (send/read/edit/delete/delete for all; group UI shows sender names over bubbles)
 9. Message Types - `PARTIAL` (text/photo/video/docs/audio/voice/circle; GIF/stickers via dedicated system missing)
 10. Reply/Quote/Threads - `PARTIAL` (reply + quote-like UI + thread panel with nested replies, no dedicated full thread navigation yet)
 11. Forwarding - `PARTIAL` (single + bulk; "without author" missing)