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/chat/ChatInput.tsx

@@ -1350,7 +1350,10 @@ export const ChatInput: React.FC<ChatInputProps> = ({ onOpenSettings, scrollToBo
 
         <form
             onSubmit={handleSubmit}
-            className="pt-0 pb-2 md:pb-4 bottom-safe-area"
+            className={cn(
+                "pt-0 pb-2 md:pb-4",
+                isMobile && isKeyboardOpen ? "ios-keyboard-safe-area" : "bottom-safe-area"
+            )}
             data-keyboard-avoid="true"
             style={isMobile && inputBarOffset > 0 && !isKeyboardOpen ? { marginBottom: `${inputBarOffset}px` } : undefined}
         >