feat(kline): 支持左右平移查看历史K线

- 初始状态：最新K线在屏幕中心（保持原有逻辑不变）
- 用户平移后可查看全部历史数据
- 切换周期时重置平移状态

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

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

@@ -64,6 +64,10 @@ 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();
@@ -130,6 +134,8 @@ 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;
     }
   }
 
@@ -496,23 +502,27 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
     );
   }
 
-  // 手势处理 - 大厂标准做法：基于像素的滚动和缩放
+  // 手势处理
   void _onScaleStart(ScaleStartDetails details) {
     _prevCandleWidth = _candleWidth;
-    _startScrollX = _scrollX;
     _startFocalPoint = details.focalPoint;
-    // 检测是否为两指缩放（pointerCount > 1表示多指触摸）
     _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;
   }
 
   void _onScaleUpdate(ScaleUpdateDetails details) {
     setState(() {
-      // 两指缩放：调整K线宽度，围绕焦点缩放
-      // 只有在明确是缩放模式（多指触摸）时才进行缩放
+      // 两指缩放
       if (_isScaling) {
         final newCandleWidth = (_prevCandleWidth * details.scale).clamp(_minCandleWidth, _maxCandleWidth);
 
-        // 围绕焦点缩放：调整滚动位置以保持焦点处的K线位置不变
         if (_startFocalPoint != null && _chartWidth > 0) {
           final focalRatio = _startFocalPoint!.dx / _chartWidth;
           final oldFocalIndex = (_startScrollX + _startFocalPoint!.dx) / _prevCandleWidth;
@@ -524,12 +534,15 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
         }
 
         _candleWidth = newCandleWidth;
+        _userHasPanned = true;  // 缩放后也标记为已操作
       } else if (_startFocalPoint != null) {
-        // 单指平移 - 直接使用像素位移
+        // 单指平移
         final dx = details.focalPoint.dx - _startFocalPoint!.dx;
-        final totalWidth = widget.klines.length * _candleWidth;
-        final maxScroll = math.max(0.0, totalWidth - _chartWidth);
+        // 最大滚动位置：让最新K线在屏幕中心
+        final int halfScreenCount = (_chartWidth / 2 / _candleWidth).ceil();
+        final double maxScroll = math.max(0.0, (widget.klines.length - halfScreenCount) * _candleWidth);
         _scrollX = (_startScrollX - dx).clamp(0.0, maxScroll);
+        _userHasPanned = true;
       }
     });
   }
@@ -569,7 +582,6 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
   }
 
   // 数据处理 - 计算要显示的K线数据
-  // 逻辑：最新K线在屏幕中心，只取中心到左边缘能显示的数量
   _VisibleData _getVisibleData(double chartWidth) {
     if (widget.klines.isEmpty || chartWidth == 0) {
       return _VisibleData(klines: [], startIndex: 0, candleWidth: _candleWidth);
@@ -578,7 +590,7 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
     // 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();
 
-    // 数据量不够半屏时，显示全部
+    // 数据量不够半屏时，显示全部，从左开始
     if (widget.klines.length <= halfScreenCount) {
       return _VisibleData(
         klines: widget.klines,
@@ -587,13 +599,26 @@ class _KlineChartWidgetState extends State<KlineChartWidget> {
       );
     }
 
-    // 数据量足够时，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
+    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,
+      );
+    }
   }
 
   int _getVisibleCount() {