feat(chat): load older messages on scroll-to-top (history pagination) (v1.11.0+15)

Repository keeps one live Timeline per room and re-yields on its
onUpdate callback (fires for both live events AND requestHistory),
not just onSync which never fires for pagination. loadMoreMessages
now paginates that same instance; added canLoadMore.

Timeline widget requests older history when scrolled within 400px of
the oldest end, guarded against re-entry, with a top loading spinner.

Verified: widget test drives a drag-to-top and asserts loadMoreMessages
fires; live smoke test confirms the onUpdate delivery path (reused by
history) still shows new messages after the refactor.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/core/config/app_config.dart

@@ -11,7 +11,7 @@ abstract final class AppConfig {
     'turns:matrix.m8chat.au:5349',
   ];
   static const String appName = 'M8Chat';
-  static const String appVersion = '1.10.0';
+  static const String appVersion = '1.11.0';
 
   // Jitsi conferencing
   static const String jitsiDomain = 'conf.m8chat.au';