fix(player): 键盘收起后保持评论输入弹窗位置

lib/pages/player/widgets/comment_composer_sheet.dart

@@ -39,6 +39,7 @@ class _CommentComposerSheetState extends State<CommentComposerSheet> {
   final _input = TextEditingController();
   final _inputFocus = FocusNode();
   final _keyboardInset = KeyboardInsetNotifier.instance;
+  double _pinnedKeyboardInset = 0;
   bool _closing = false;
 
   @override
@@ -114,7 +115,8 @@ class _CommentComposerSheetState extends State<CommentComposerSheet> {
 
   @override
   Widget build(BuildContext context) {
-    final keyboardHeight = _keyboardHeight(context);
+    final currentKeyboardInset = _keyboardHeight(context);
+    _pinnedKeyboardInset = math.max(_pinnedKeyboardInset, currentKeyboardInset);
     final l10n = AppLocalizations.of(context)!;
     final signedIn = context.watch<AuthController>().isSignedIn;
     final hasContent = _input.text.trim().isNotEmpty;
@@ -139,7 +141,7 @@ class _CommentComposerSheetState extends State<CommentComposerSheet> {
           child: AnimatedPadding(
             duration: const Duration(milliseconds: 200),
             curve: Curves.easeOut,
-            padding: EdgeInsets.only(bottom: keyboardHeight),
+            padding: EdgeInsets.only(bottom: _pinnedKeyboardInset),
             child: GestureDetector(
               behavior: HitTestBehavior.opaque,
               onTap: () {},