refactor: 重构聊天数据层至core并简化首页UI

apps/lib/features/home/presentation/screens/home_screen.dart

@@ -393,12 +393,6 @@ class _HomeScreenState extends State<HomeScreen>
     try {
       if (hasEarlierHistory) {
         await _loadMoreHistoryPreservingViewport(chatBloc);
-      } else {
-        Toast.show(
-          context,
-          context.l10n.homeNoEarlierHistory,
-          type: ToastType.info,
-        );
       }
       _applyViewportDecision(
         _dispatchViewportEvent(
@@ -687,29 +681,6 @@ class _HomeEmptyStateAmbient extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final colorScheme = Theme.of(context).colorScheme;
-
-    return Center(
-      child: IgnorePointer(
-        child: Container(
-          key: homeEmptyStateAmbientKey,
-          width: double.infinity,
-          height: AppSpacing.xxl * 6,
-          margin: const EdgeInsets.symmetric(horizontal: AppSpacing.xxl),
-          decoration: BoxDecoration(
-            borderRadius: BorderRadius.circular(AppSpacing.xxl * 2),
-            gradient: LinearGradient(
-              begin: Alignment.centerLeft,
-              end: Alignment.centerRight,
-              colors: [
-                colorScheme.primaryContainer.withValues(alpha: 0.12),
-                colorScheme.primary.withValues(alpha: 0.08),
-                colorScheme.primaryContainer.withValues(alpha: 0.12),
-              ],
-            ),
-          ),
-        ),
-      ),
-    );
+    return const SizedBox.shrink(key: homeEmptyStateAmbientKey);
   }
 }