style: increase aside width and ad image size

- 增加右侧 aside 宽度从 256px 到 300px
- 增加广告图片宽度从 200px 到 280px

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/.vitepress/theme/DynamicAds.vue

@@ -64,7 +64,7 @@ onUnmounted(() => {
 
 .ad-image {
   max-width: 100%;
-  width: 200px;
+  width: 280px;
   height: auto;
   margin-bottom: 0.5rem;
 }

docs/.vitepress/theme/custom.css

@@ -6,4 +6,5 @@
 :root {
   --vp-sidebar-width: 285px;
   --vp-sidebar-bg-color: var(--vp-c-bg-alt);
-}
+  --vp-aside-width: 300px;
+}