refactor: simplify mobile keyboard handling

Removed fragile global keyboard viewport manager
Restored native mobile viewport behavior
Fixed textarea content shifting outside inputs

packages/ui/src/components/chat/ChatInput.tsx

@@ -792,7 +792,6 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
     const agents = getVisibleAgents();
     const primaryAgents = React.useMemo(() => agents.filter((agent) => agent.mode === 'primary'), [agents]);
     const isMobile = useUIStore((state) => state.isMobile);
-    const isKeyboardOpen = useUIStore((state) => state.isKeyboardOpen);
     const inputBarOffset = useUIStore((state) => state.inputBarOffset);
     const persistChatDraft = useUIStore((state) => state.persistChatDraft);
     const inputSpellcheckEnabled = useUIStore((state) => state.inputSpellcheckEnabled);
@@ -3303,10 +3302,9 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
             className={cn(
                 "relative pt-0 pb-4",
                 isDesktopExpanded && 'flex h-full min-h-0 flex-col pt-4',
-                isMobile && (isKeyboardOpen ? 'ios-keyboard-safe-area' : 'bottom-safe-area')
+                isMobile && 'bottom-safe-area'
             )}
-            data-keyboard-avoid="none"
-            style={isMobile && inputBarOffset > 0 && !isKeyboardOpen ? { marginBottom: `${inputBarOffset}px` } : undefined}
+            style={isMobile && inputBarOffset > 0 ? { marginBottom: `${inputBarOffset}px` } : undefined}
         >
             <div className={cn('chat-column relative overflow-visible', isDesktopExpanded && 'flex flex-1 min-h-0 flex-col')}>
                 <AttachedFilesList />