chore(assets): migrate local images to remote storage

- Replace local image paths with remote URLs in components, content, and config.
- Remove local image files from the public directory to reduce repository size.
- Add dark mode support for the hero background image in `index.vue`.

app/pages/index.vue

@@ -2,14 +2,8 @@
   <UPage>
     <!-- Hero Banner -->
     <UPageHero
-      class="bg-cover bg-center"
-      style="
-        background-image: url(&quot;/hero-image-2.jpg?v=2&quot;);
-        background-position-y: -40px;
-        background-repeat: no-repeat;
-        background-color: rgba(255, 255, 255, 0.5); /* Semi-transparent black */
-        background-blend-mode: lighten;
-      "
+      :class="heroClass"
+      :style="heroStyle"
       title="连接校友 · 传承精神"
       description="马来西亚柔佛永平中学校友会官方网站"
       :links="heroCta"
@@ -40,6 +34,20 @@ useSeoMeta({
   title: "首页",
 });
 
+const colorMode = useColorMode()
+const heroClass = 'bg-cover bg-center'
+const heroStyle = computed(() => ({
+  backgroundImage: colorMode.value === 'dark' 
+    ? 'url("https://img.yphsalumni.org/i/2025/11/28/qzxrpq.png")'
+    : 'url("https://img.yphsalumni.org/i/2025/11/28/qk9fe8.png")',
+  backgroundPositionY: '-40px',
+  backgroundRepeat: 'no-repeat',
+  backgroundColor: colorMode.value === 'dark' 
+    ? 'rgba(0, 0, 0, 0.5)' 
+    : 'rgba(255, 255, 255, 0.5)',
+  backgroundBlendMode: colorMode.value === 'dark' ? 'darken' : 'lighten'
+}))
+
 const heroCta = ref([
   {
     label: "立即加入我们",