fix: HiChart用canvas自身getBoundingClientRect获取渲染尺寸，消除CSS拉伸导致的线条变形

plugins/sentinel/dashboard.html

@@ -157,12 +157,12 @@
       window.addEventListener('resize', function(){ self._resize(); });
     }
     HiChart.prototype._resize = function() {
-      var rect = this.canvas.parentElement.getBoundingClientRect();
+      // 用 canvas 自身的 CSS 渲染尺寸 → 内部分辨率 = CSS尺寸 × DPR (保持高清)
-      var w = Math.max(rect.width - 8, 100);
+      var box = this.canvas.getBoundingClientRect();
-      var h = 60;
+      var w = box.width, h = box.height;
+      if (w <= 0 || h <= 0) { w = 280; h = 60; }  // fallback
       this.canvas.width = w * this._dpr;
       this.canvas.height = h * this._dpr;
-      // CSS controls display size via width:100%;height:60px
       this.ctx.setTransform(this._dpr, 0, 0, this._dpr, 0, 0);
       this._draw();
     };