回退 debTemps 首尾填充，修复 canvas CSS 无尺寸导致的图表缩塌

- 首尾填充会画成水平直线不反映预测，回退；past_days=1 已从后端补齐全天数据
- canvas 保留 width/height:100% 但去掉 !important，Chart.js 自管分辨率

frontend/components/dashboard/DetailPanelContent.module.css

@@ -107,6 +107,8 @@
 
 .root :global(.detail-mini-chart canvas) {
   display: block;
+  width: 100%;
+  height: 100%;
 }
 
 .root :global(.detail-mini-chart-legend) {

frontend/components/dashboard/FutureForecastModal.module.css

@@ -786,6 +786,8 @@
 
 .root :global(.intraday-scene-frame canvas) {
   display: block;
+  width: 100%;
+  height: 100%;
 }
 
 .root :global(.intraday-scene-legend) {

frontend/components/dashboard/ScanTerminalCard.module.css

@@ -1061,6 +1061,8 @@
 
 .root :global(.scan-ai-city-chart canvas) {
   display: block;
+  width: 100%;
+  height: 100%;
 }
 
 .root :global(.scan-ai-city-chart-placeholder) {

frontend/lib/chart-utils.ts

@@ -411,17 +411,6 @@ export function getTemperatureChartData(
       ? Number((temp + offset).toFixed(1))
       : null,
   );
-  const firstValid = debTemps.findIndex((t) => t != null);
-  const lastValid = (() => {
-    for (let i = debTemps.length - 1; i >= 0; i--) {
-      if (debTemps[i] != null) return i;
-    }
-    return -1;
-  })();
-  if (firstValid >= 0 && lastValid >= 0) {
-    for (let i = 0; i < firstValid; i++) debTemps[i] = debTemps[firstValid];
-    for (let i = lastValid + 1; i < debTemps.length; i++) debTemps[i] = debTemps[lastValid];
-  }
   const debPast = debTemps.map((temp, index) =>
     currentIndex >= 0 && index <= currentIndex ? temp : null,
   );