fix(android): 修复国产手机 WebView 中本地图片/视频选择无效的问题

- 将 .file-input-hidden 从 display:none 改为 opacity:0 + position:absolute
  国产手机（华为/小米/OPPO/vivo）WebView 对 display:none 的 input[type=file]
  选择后不会填充 files 属性，导致 change 事件触发但 files 为空
- 在 ImagePicker/VideoPicker 的 change 事件中增加空文件警告日志
- 在 upload.ts handleLocalImageFiles/handleLocalVideoFiles 中增加空文件
  时的 Toast 提示，避免静默失败

static/src/app/methods/upload.ts

@@ -78,6 +78,11 @@ export const uploadMethods = {
     }
     const list = this.normalizeLocalFiles(files);
     if (!list.length) {
+      this.uiPushToast({
+        title: '未获取到文件',
+        message: '系统未返回有效的文件内容，请重试',
+        type: 'warning'
+      });
       return;
     }
     const existingCount = Array.isArray(this.selectedImages) ? this.selectedImages.length : 0;
@@ -139,6 +144,11 @@ export const uploadMethods = {
     }
     const list = this.normalizeLocalFiles(files);
     if (!list.length) {
+      this.uiPushToast({
+        title: '未获取到文件',
+        message: '系统未返回有效的文件内容，请重试',
+        type: 'warning'
+      });
       return;
     }
     const valid = list.filter((file) => this.isVideoFile(file));

static/src/components/overlay/ImagePicker.vue

@@ -117,7 +117,11 @@ const triggerLocal = () => {
 
 const onLocalChange = (event: Event) => {
   const target = event.target as HTMLInputElement;
-  emit('local-files', target?.files || null);
+  const files = target?.files || null;
+  if (!files || files.length === 0) {
+    console.warn('[ImagePicker] change fired but files empty — likely WebView compat issue');
+  }
+  emit('local-files', files);
   if (target) {
     target.value = '';
   }

static/src/components/overlay/VideoPicker.vue

@@ -119,7 +119,11 @@ const triggerLocal = () => {
 
 const onLocalChange = (event: Event) => {
   const target = event.target as HTMLInputElement;
-  emit('local-files', target?.files || null);
+  const files = target?.files || null;
+  if (!files || files.length === 0) {
+    console.warn('[VideoPicker] change fired but files empty — likely WebView compat issue');
+  }
+  emit('local-files', files);
   if (target) {
     target.value = '';
   }

static/src/styles/components/input/_composer.scss

@@ -805,7 +805,11 @@ body[data-theme='light'] {
 }
 
 .file-input-hidden {
-    display: none;
+    position: absolute;
+    opacity: 0;
+    width: 0;
+    height: 0;
+    pointer-events: none;
 }
 
 .quick-menu {