feat: move legend to top-right box with hover highlighting

- Move legend from bottom to vertical top-right box with background
- Highlight hovered category in legend (bold text, others dimmed)
- Dim legend color swatches to 0.15 opacity for non-hovered items
- Make drill-down title larger (22px bold centered)
- Reserve right margin (180px) for legend, free up bottom space

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app.js

@@ -614,9 +614,14 @@ function buildTimelineOption(drillCategory) {
 
     const chartTitle = drillCategory ? {
         text: '← ' + drillCategory,
-        left: 20,
-        top: 10,
-        textStyle: { fontSize: 16, fontWeight: 500, color: '#555' },
+        left: 'center',
+        top: 6,
+        textStyle: {
+            fontSize: 22,
+            fontWeight: 'bold',
+            fontFamily: '-apple-system, BlinkMacSystemFont, "SF Pro", "Segoe UI", system-ui, sans-serif',
+            color: '#333'
+        },
         triggerEvent: true
     } : { show: false };
 
@@ -626,18 +631,23 @@ function buildTimelineOption(drillCategory) {
         tooltip: { show: false },
         legend: {
             data: legendData,
-            bottom: 0,
-            left: 'center',
-            itemWidth: 14,
-            itemHeight: 14,
+            top: drillCategory ? 42 : 10,
+            right: 10,
+            orient: 'vertical',
+            itemWidth: 12,
+            itemHeight: 12,
             textStyle: { fontSize: 13 },
-            itemGap: 16
+            itemGap: 8,
+            backgroundColor: 'rgba(255,255,255,0.85)',
+            borderRadius: 6,
+            padding: [8, 12],
+            selector: false
         },
         grid: {
             left: 30,
-            right: 30,
-            top: drillCategory ? 50 : 40,
-            bottom: 50,
+            right: 180,
+            top: drillCategory ? 55 : 40,
+            bottom: 30,
             containLabel: true
         },
         xAxis: {
@@ -675,23 +685,41 @@ function renderTimelineChart(drillCategory) {
     myChart.setOption(tlOption, true);
 
     // Highlight entire series on hover so all bars show emphasis.label
+    // Also highlight the corresponding legend item
+    const legendNames = tlOption.legend.data;
     let hlSeries = null;
+
+    function updateLegend(activeName) {
+        myChart.setOption({
+            legend: {
+                data: legendNames.map(name => {
+                    if (!activeName) return { name, textStyle: { fontWeight: 'normal', color: '#333' }, itemStyle: { opacity: 1 } };
+                    if (name === activeName) return { name, textStyle: { fontWeight: 'bold', color: '#333' }, itemStyle: { opacity: 1 } };
+                    return { name, textStyle: { fontWeight: 'normal', color: '#ccc' }, itemStyle: { opacity: 0.15 } };
+                })
+            }
+        });
+    }
+
     myChart.on('mouseover', function(params) {
         if (params.componentType !== 'series' || params.seriesName === '__total__') return;
         if (hlSeries === params.seriesName) return;
         if (hlSeries) myChart.dispatchAction({ type: 'downplay', seriesName: hlSeries });
         hlSeries = params.seriesName;
         myChart.dispatchAction({ type: 'highlight', seriesName: params.seriesName });
+        updateLegend(params.seriesName);
     });
     myChart.on('mouseout', function(params) {
         if (params.componentType !== 'series' || !hlSeries) return;
         myChart.dispatchAction({ type: 'downplay', seriesName: hlSeries });
         hlSeries = null;
+        updateLegend(null);
     });
     myChart.on('globalout', function() {
         if (hlSeries) {
             myChart.dispatchAction({ type: 'downplay', seriesName: hlSeries });
             hlSeries = null;
+            updateLegend(null);
         }
     });