Feat 为画廊模式添加每页显示图片数量的配置 (#82)

* Feat: Add dynamic image-per-page configuration for gallery mode

- Implemented a slider to configure the number of images displayed per page (1-5) in gallery mode.
- Updated the reader to dynamically reflect changes in the `imagesPerPage` setting without requiring a mode switch or reopening.
- Ensured compatibility with existing continuous reading mode.

* fix currentImagesPerPage

* fix Continuous mode

* improve readerScreenPicNumber setting disable view

* improve PhotoViewController

lib/pages/reader/reader.dart

@@ -1,6 +1,7 @@
 library venera_reader;
 
 import 'dart:async';
+import 'dart:math' as math;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
@@ -82,7 +83,8 @@ class _ReaderState extends State<Reader> with _ReaderLocation, _ReaderWindow {
   }
 
   @override
-  int get maxPage => images?.length ?? 1;
+  int get maxPage =>
+      ((images?.length ?? 1) + imagesPerPage - 1) ~/ imagesPerPage;
 
   ComicType get type => widget.type;
 
@@ -94,6 +96,30 @@ class _ReaderState extends State<Reader> with _ReaderLocation, _ReaderWindow {
 
   late ReaderMode mode;
 
+  int get imagesPerPage => appdata.settings['readerScreenPicNumber'] ?? 1;
+
+  int _lastImagesPerPage = appdata.settings['readerScreenPicNumber'] ?? 1;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    _checkImagesPerPageChange();
+  }
+
+  void _checkImagesPerPageChange() {
+    int currentImagesPerPage = imagesPerPage;
+    if (_lastImagesPerPage != currentImagesPerPage) {
+      _adjustPageForImagesPerPageChange(_lastImagesPerPage, currentImagesPerPage);
+      _lastImagesPerPage = currentImagesPerPage;
+    }
+  }
+
+  void _adjustPageForImagesPerPageChange(int oldImagesPerPage, int newImagesPerPage) {
+    int previousImageIndex = (page - 1) * oldImagesPerPage;
+    int newPage = (previousImageIndex ~/ newImagesPerPage) + 1;
+    page = newPage;
+  }
+
   History? history;
 
   @override
@@ -133,6 +159,7 @@ class _ReaderState extends State<Reader> with _ReaderLocation, _ReaderWindow {
 
   @override
   Widget build(BuildContext context) {
+    _checkImagesPerPageChange();
     return KeyboardListener(
       focusNode: focusNode,
       autofocus: true,