fix: add position: relative to scroll-view for correct offsetTop

Without position: relative, .task-item offsetParent is the body element,
causing offsetTop to be measured from document root rather than the
scroll container. This makes scrollToTask calculate wrong scrollTop.

static/css/tasks.css

@@ -44,6 +44,7 @@
     flex: 1;
     height: 600px;
     overflow-y: auto;
+    position: relative;
     background: white;
     border-radius: 8px;
     box-shadow: 0 2px 4px rgba(0,0,0,0.1);