fix(health,miniprogram): 轮播图图片改用相对路径 + wx.downloadFile 解决 HTTP 限制

问题：微信小程序 <image> 不支持 HTTP URL，签名 URL 与 upload 中间件不兼容。
修复：
1. 公开轮播图 API 返回相对路径（/uploads/...）而非签名 URL
2. 小程序用 wx.downloadFile 下载图片后使用本地临时路径
3. 移除 banner_handler 中不再需要的 base_url/Host header 逻辑

apps/miniprogram/src/pages/index/index.tsx

@@ -30,6 +30,8 @@ interface PublicBanner {
   image_url?: string;
   link_type?: string;
   link_target?: string;
+  /** 下载后的本地临时路径 */
+  local_path?: string;
 }
 
 // ─── 访客首页 ───
@@ -67,7 +69,22 @@ function GuestHome({ modeClass }: { modeClass: string }) {
       ]);
 
       if (bannerData.status === 'fulfilled' && bannerData.value?.length > 0) {
-        setBanners(bannerData.value);
+        const baseUrl = process.env.TARO_APP_API_URL || 'http://localhost:3000/api/v1';
+        const fileBase = baseUrl.replace(/\/api\/v1$/, '');
+        const withLocal = await Promise.all(
+          bannerData.value.map(async (b) => {
+            if (!b.image_url) return b;
+            try {
+              const fullUrl = b.image_url.startsWith('http') ? b.image_url : `${fileBase}${b.image_url}`;
+              const res = await Taro.downloadFile({ url: fullUrl });
+              if (res.tempFilePath) {
+                return { ...b, local_path: res.tempFilePath };
+              }
+            } catch { /* ignore */ }
+            return b;
+          })
+        );
+        setBanners(withLocal);
       } else {
         setBanners(FALLBACK_SLIDES);
       }
@@ -98,8 +115,8 @@ function GuestHome({ modeClass }: { modeClass: string }) {
         {slides.map((slide, idx) => (
           <SwiperItem key={slide.id || idx}>
             <View className='guest-slide'>
-              {slide.image_url ? (
-                <Image className='guest-slide-image' src={slide.image_url} mode='aspectFill' />
+              {(slide.local_path || slide.image_url) ? (
+                <Image className='guest-slide-image' src={slide.local_path || slide.image_url} mode='aspectFill' />
               ) : (
                 <View className={`guest-slide-bg guest-slide-bg--${(idx % 3) + 1}`} />
               )}