feat: 将截图上传逻辑从直接文件上传改为客户端base64编码处理，并增加了图片类型校验。

frontend/js/main.js

@@ -3238,35 +3238,45 @@ document.addEventListener("DOMContentLoaded", function () {
     input.addEventListener("change", async function () {
       if (!this.files.length) return;
 
-      const formData = new FormData();
-      for (const file of this.files) {
-        formData.append("screenshots", file);
-      }
+      const files = Array.from(this.files);
+      const newBase64Images = [];
 
-      try {
-        const response = await authenticatedFetch("/api/upload", {
-          method: "POST",
-          body: formData,
-        });
-
-        if (response.ok) {
-          const data = await response.json();
-          const filePaths = data.filePaths || [];
-
-          if (type === "create") {
-            createUploadedScreenshots = [
-              ...createUploadedScreenshots,
-              ...filePaths,
-            ];
-            renderScreenshotPreviews("create", createUploadedScreenshots);
-          } else {
-            editUploadedScreenshots = [...editUploadedScreenshots, ...filePaths];
-            renderScreenshotPreviews("edit", editUploadedScreenshots);
-          }
+      for (const file of files) {
+        // 验证是否为图片
+        if (!file.type.startsWith("image/")) {
+          console.warn(`File is not an image: ${file.name}`);
+          continue;
+        }
+
+        try {
+          const base64 = await new Promise((resolve, reject) => {
+            const reader = new FileReader();
+            reader.onload = () => resolve(reader.result);
+            reader.onerror = (error) => reject(error);
+            reader.readAsDataURL(file);
+          });
+          newBase64Images.push(base64);
+        } catch (error) {
+          console.error(`Error converting file ${file.name} to base64:`, error);
         }
-      } catch (error) {
-        console.error("Error uploading screenshots:", error);
       }
+
+      if (type === "create") {
+        createUploadedScreenshots = [
+          ...createUploadedScreenshots,
+          ...newBase64Images,
+        ];
+        renderScreenshotPreviews("create", createUploadedScreenshots);
+      } else {
+        editUploadedScreenshots = [
+          ...editUploadedScreenshots,
+          ...newBase64Images,
+        ];
+        renderScreenshotPreviews("edit", editUploadedScreenshots);
+      }
+
+      // 清除 input，以便再次选择同一张图片
+      this.value = "";
     });
   }