feat(chat): scroll-to-latest button + panic hold-progress ring (v1.10.0+14)

B6 scroll-to-latest: ScrollController on the timeline; a small
  arrow-down FAB fades in once scrolled >400px up and animates back
  to the newest message on tap (overlaid on the list, not the FAB slot)
B5 panic hold-ring: 700ms AnimationController drives a red progress
  ring around the panic icon; haptic + fire on completion, silent
  reset on early release; tap-hint and configured guard preserved

Panic ring verified in-browser (ring fills, alert fires to the room).
Scroll-to-latest verified with a deterministic widget test because the
CanvasKit surface rejects synthetic scroll input in headless Chromium.

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 = '1.9.0';
+  static const String appVersion = '1.10.0';
 
   // Jitsi conferencing
   static const String jitsiDomain = 'conf.m8chat.au';