fix(mobile): add iOS keyboard home indicator safe area (#141)

On iOS devices, when the keyboard is open, there's a home indicator bar
(approximately 34px tall) at the bottom of the keyboard that needs additional
safe area padding.

Changes:
- Add --oc-keyboard-home-indicator CSS variable
- Add ios-keyboard-safe-area class for keyboard open state
- Detect iOS userAgent and set keyboard home indicator height
- Apply ios-keyboard-safe-area class to ChatInput when keyboard is open

Co-authored-by: Jovines <jovines@qq.com>

packages/ui/src/components/layout/MainLayout.tsx

@@ -201,6 +201,10 @@ export const MainLayout: React.FC = () => {
             root.style.setProperty('--oc-keyboard-inset', `${stickyKeyboardInset}px`);
             previousHeight = height;
 
+            const isIOS = /iPad|iPhone|iPod/.test(navigator.userAgent);
+            const keyboardHomeIndicator = isIOS && stickyKeyboardInset > 0 ? 34 : 0;
+            root.style.setProperty('--oc-keyboard-home-indicator', `${keyboardHomeIndicator}px`);
+
             const avoidTarget = isTextTarget ? resolveKeyboardAvoidTarget(active) : null;
 
             if (!isMobile || !avoidTarget || !active) {