fix(kline): simplify pan logic - scrollX now always controls view position

- Removed _userHasPanned flag and special handling
- _scrollX is initialized in _scrollToCenter() at startup
- Pan gesture directly modifies _scrollX
- _getVisibleData() always uses _scrollX to calculate visible range

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mining-app/lib/presentation/widgets/kline_chart/kline_chart_widget.dart

@@ -64,10 +64,6 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
   bool _showCrossLine = false;
   int _crossLineIndex = -1;
 
-  // 平移控制：用户是否已手动平移
-  bool _userHasPanned = false;
-  int _panStartIndex = 0;  // 平移开始时的起始索引
-
   @override
   void initState() {
     super.initState();
@@ -98,25 +94,23 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
   ///
   /// 计算逻辑：
   /// - K线从左边开始排列
-  /// - 数据不够时（总宽度 <= 屏幕宽度），不滚动，有多少显示多少
+  /// - 数据不够时（总宽度 <= 屏幕宽度的一半），不滚动，有多少显示多少
   /// - 数据量大时，计算滚动位置让最新K线在屏幕中心
   void _scrollToCenter() {
     if (widget.klines.isEmpty || _chartWidth == 0) return;
 
-    final totalWidth = widget.klines.length * _candleWidth;
+    // 计算屏幕中心到左边缘能显示多少根K线
+    final int halfScreenCount = (_chartWidth / 2 / _candleWidth).ceil();
 
-    if (totalWidth <= _chartWidth) {
-      // 数据不够，不滚动，从左开始显示
+    if (widget.klines.length <= halfScreenCount) {
+      // 数据不够半屏，不滚动，从左开始显示
       _scrollX = 0;
     } else {
-      // 数据量大，计算让最新K线在屏幕中心的滚动位置
-      // 最新K线的中心位置 = (K线数量 - 0.5) * 单根K线宽度
-      final lastKlineCenter = (widget.klines.length - 0.5) * _candleWidth;
-      // 目标滚动位置 = 最新K线中心 - 屏幕宽度的一半
-      final targetScroll = lastKlineCenter - _chartWidth / 2;
-      // 限制在有效滚动范围内
-      final maxScroll = totalWidth - _chartWidth;
-      _scrollX = targetScroll.clamp(0.0, maxScroll);
+      // 数据量足够，滚动使最新K线在屏幕中心
+      // startIndex = klines.length - halfScreenCount
+      // scrollX = startIndex * candleWidth
+      final int startIndex = widget.klines.length - halfScreenCount;
+      _scrollX = startIndex * _candleWidth;
     }
   }
 
@@ -134,7 +128,6 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
     // 当 K 线数据变化时，重新初始化
     if (oldWidget.klines.length != widget.klines.length) {
       _initialized = false;
-      _userHasPanned = false;  // 重置平移状态
       _scrollX = 0;
     }
   }
@@ -507,13 +500,6 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
     _prevCandleWidth = _candleWidth;
     _startFocalPoint = details.focalPoint;
     _isScaling = details.pointerCount > 1;
-
-    // 如果是首次平移，需要初始化 _scrollX
-    if (!_userHasPanned && !_isScaling) {
-      final int halfScreenCount = (_chartWidth / 2 / _candleWidth).ceil();
-      final int startIndex = math.max(0, widget.klines.length - halfScreenCount);
-      _scrollX = startIndex * _candleWidth;
-    }
     _startScrollX = _scrollX;
   }
 
@@ -527,14 +513,13 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
           final focalRatio = _startFocalPoint!.dx / _chartWidth;
           final oldFocalIndex = (_startScrollX + _startFocalPoint!.dx) / _prevCandleWidth;
           final newFocalX = oldFocalIndex * newCandleWidth;
-          _scrollX = (newFocalX - focalRatio * _chartWidth).clamp(
-            0.0,
-            math.max(0.0, widget.klines.length * newCandleWidth - _chartWidth),
-          );
+          // 缩放后重新计算maxScroll
+          final int halfScreenCount = (_chartWidth / 2 / newCandleWidth).ceil();
+          final double maxScroll = math.max(0.0, (widget.klines.length - halfScreenCount) * newCandleWidth);
+          _scrollX = (newFocalX - focalRatio * _chartWidth).clamp(0.0, maxScroll);
         }
 
         _candleWidth = newCandleWidth;
-        _userHasPanned = true;  // 缩放后也标记为已操作
       } else if (_startFocalPoint != null) {
         // 单指平移
         // dx > 0 向右滑（看更早历史），dx < 0 向左滑（看更新数据）
@@ -544,7 +529,6 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
         final double maxScroll = math.max(0.0, (widget.klines.length - halfScreenCount) * _candleWidth);
         // 向右滑 dx>0，scrollX 减小，显示更早的数据
         _scrollX = (_startScrollX - dx).clamp(0.0, maxScroll);
-        _userHasPanned = true;
 
         // DEBUG: 打印滚动信息
         debugPrint('Pan: dx=$dx, scrollX=$_scrollX, maxScroll=$maxScroll, startIndex=${(_scrollX / _candleWidth).floor()}');
@@ -592,6 +576,8 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
       return _VisibleData(klines: [], startIndex: 0, candleWidth: _candleWidth);
     }
 
+    // 计算屏幕能显示多少根K线
+    final int fullScreenCount = (chartWidth / _candleWidth).ceil() + 1;
     // 计算屏幕中心到左边缘能显示多少根K线
     final int halfScreenCount = (chartWidth / 2 / _candleWidth).ceil();
 
@@ -604,26 +590,15 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
       );
     }
 
-    // 数据量足够时
-    if (_userHasPanned) {
-      // 用户已平移，根据 _scrollX 计算起始索引
-      final int fullScreenCount = (chartWidth / _candleWidth).ceil() + 1;
-      final int startIndex = (_scrollX / _candleWidth).floor().clamp(0, widget.klines.length - 1);
-      final int endIndex = math.min(startIndex + fullScreenCount, widget.klines.length);
-      return _VisibleData(
-        klines: widget.klines.sublist(startIndex, endIndex),
-        startIndex: startIndex,
-        candleWidth: _candleWidth,
-      );
-    } else {
-      // 初始状态：只取最近的 halfScreenCount 根，让最新那根在屏幕中心
-      final int startIndex = widget.klines.length - halfScreenCount;
-      return _VisibleData(
-        klines: widget.klines.sublist(startIndex),
-        startIndex: startIndex,
-        candleWidth: _candleWidth,
-      );
-    }
+    // 数据量足够时，根据 _scrollX 计算起始索引
+    final int startIndex = (_scrollX / _candleWidth).floor().clamp(0, math.max(0, widget.klines.length - 1));
+    final int endIndex = math.min(startIndex + fullScreenCount, widget.klines.length);
+
+    return _VisibleData(
+      klines: widget.klines.sublist(startIndex, endIndex),
+      startIndex: startIndex,
+      candleWidth: _candleWidth,
+    );
   }
 
   int _getVisibleCount() {