feat(kline): add dynamic X-axis time labels

- Added _drawTimeAxis method to render time labels
- Labels dynamically adjust spacing based on candleWidth
- Shows HH:MM format, or M/D for midnight
- Labels follow pan/zoom movements
- Increased bottomPadding to 20px for label space

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

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

@@ -54,7 +54,7 @@ class KlinePainter extends CustomPainter {
     const leftPadding = 8.0;
     const rightPadding = 50.0;
     const topPadding = 20.0;
-    const bottomPadding = 8.0;
+    const bottomPadding = 20.0;  // 增加底部空间用于时间刻度
 
     final chartWidth = size.width - leftPadding - rightPadding;
     final chartHeight = size.height - topPadding - bottomPadding;
@@ -235,6 +235,9 @@ class KlinePainter extends CustomPainter {
       _drawCrossLine(canvas, size, crossLineIndex, leftPadding, actualCandleWidth, priceToY, scrollOffset);
     }
 
+    // 绘制时间轴
+    _drawTimeAxis(canvas, size, leftPadding, rightPadding, bottomPadding, actualCandleWidth, scrollOffset);
+
     // 绘制MA图例
     _drawLegend(canvas, size, leftPadding, topPadding);
   }
@@ -280,6 +283,77 @@ class KlinePainter extends CustomPainter {
     }
   }
 
+  void _drawTimeAxis(
+    Canvas canvas,
+    Size size,
+    double leftPadding,
+    double rightPadding,
+    double bottomPadding,
+    double candleWidth,
+    double scrollOffset,
+  ) {
+    if (klines.isEmpty) return;
+
+    final textPainter = TextPainter(textDirection: ui.TextDirection.ltr);
+    final drawableWidth = size.width - leftPadding - rightPadding;
+
+    // 根据K线宽度动态计算时间标签间隔
+    // 目标：标签之间至少间隔60像素
+    final minLabelSpacing = 60.0;
+    final klinePerLabel = (minLabelSpacing / candleWidth).ceil();
+    // 确保间隔是合理的数字（5, 10, 15, 20, 30, 60等）
+    final intervals = [5, 10, 15, 20, 30, 60, 120, 240];
+    int labelInterval = intervals.firstWhere(
+      (i) => i >= klinePerLabel,
+      orElse: () => klinePerLabel,
+    );
+
+    // 计算可见区域的起始和结束索引
+    final startIndex = (scrollOffset / candleWidth).floor();
+    final endIndex = ((scrollOffset + drawableWidth) / candleWidth).ceil();
+
+    // 找到第一个应该显示标签的索引（对齐到间隔）
+    final firstLabelIndex = ((startIndex / labelInterval).ceil()) * labelInterval;
+
+    final y = size.height - bottomPadding + 4;
+
+    for (int i = firstLabelIndex; i <= endIndex && i < klines.length; i += labelInterval) {
+      if (i < 0) continue;
+
+      final x = leftPadding + i * candleWidth + candleWidth / 2 - scrollOffset;
+
+      // 检查是否在可见区域内
+      if (x < leftPadding - 20 || x > size.width - rightPadding + 20) continue;
+
+      final time = klines[i].time;
+      final timeStr = _formatTimeLabel(time);
+
+      textPainter.text = TextSpan(
+        text: timeStr,
+        style: TextStyle(color: _textColor, fontSize: 9),
+      );
+      textPainter.layout();
+
+      // 居中绘制时间标签
+      final textX = x - textPainter.width / 2;
+      // 确保不超出边界
+      final clampedX = textX.clamp(leftPadding, size.width - rightPadding - textPainter.width);
+      textPainter.paint(canvas, Offset(clampedX, y));
+    }
+  }
+
+  String _formatTimeLabel(DateTime time) {
+    // 根据时间显示不同格式
+    // 如果是新的一天，显示日期；否则显示时间
+    final hour = time.hour.toString().padLeft(2, '0');
+    final minute = time.minute.toString().padLeft(2, '0');
+    if (time.hour == 0 && time.minute == 0) {
+      // 新的一天，显示月/日
+      return '${time.month}/${time.day}';
+    }
+    return '$hour:$minute';
+  }
+
   void _drawLine(
     Canvas canvas,
     List<double?> data,