4.B QQ 链接分享补 previewimageUrl：用 app icon 当缩略图

QQ 会话里链接分享的缩略图位空白，因为 News 类型缺 previewimageUrl 字段。
对齐 msext QQShareManager.m:517-522 + 1271-1278 的写法：

1. app icon JPEG 0.7 写到 NSTemporaryDirectory()/qq_share_<UUID>.jpg
2. 拼 file://<path> 字符串
3. base64 后再 URL-encode
4. append &previewimageUrl=<那串>

writeAppIconToTemp() 与 appIconImage() 直接抄 WechatShare 同源策略（读
Info.plist CFBundleIcons → CFBundlePrimaryIcon → CFBundleIconFiles 最后
一个）。两处复制可接受 —— Share 模块统一缩略图工具可后续抽到
ImageProvider，本次保持改动范围最小。

ylgamehall/Source/Share/QQShare.swift

@@ -114,6 +114,13 @@ public final class QQShare: SharePlatform {
             parts.append("url=\(Self.encode(Self.base64(content.webpageUrl)))")
         }
 
+        // 3. 缩略图 —— app icon 写到 tmp 目录 → previewimageUrl = urlenc(base64("file://<path>"))
+        //    对齐 msext QQShareManager.m:517-522 saveImageToTempDirectory + base64
+        if let thumbPath = Self.writeAppIconToTemp() {
+            let fileURL = "file://\(thumbPath)"
+            parts.append("previewimageUrl=\(Self.encode(Self.base64(fileURL)))")
+        }
+
         let urlString = "mqqapi://\(host)?\(parts.joined(separator: "&"))"
         Self.log.debug("QQShare URL → \(urlString, privacy: .public)")
 
@@ -184,6 +191,38 @@ public final class QQShare: SharePlatform {
         return top
     }
 
+    // MARK: - 缩略图（app icon → tmp file）
+
+    /// 把 app icon JPEG 写到 NSTemporaryDirectory，返回绝对路径。
+    /// 对齐 msext QQShareManager.m:1271-1278 saveImageToTempDirectory:
+    /// 文件名 qq_share_<UUID>.jpg，JPEG 0.7 质量。失败返回 nil。
+    private static func writeAppIconToTemp() -> String? {
+        guard let data = appIconImage().jpegData(compressionQuality: 0.7) else { return nil }
+        let path = NSTemporaryDirectory() + "qq_share_\(UUID().uuidString).jpg"
+        do {
+            try data.write(to: URL(fileURLWithPath: path), options: .atomic)
+            return path
+        } catch {
+            log.error("QQShare 写缩略图临时文件失败 \(error.localizedDescription, privacy: .public)")
+            return nil
+        }
+    }
+
+    /// app icon UIImage，与 WechatShare.appIconImage() 同源策略
+    /// （读 Info.plist CFBundleIcons → CFBundlePrimaryIcon → CFBundleIconFiles 最后一个）
+    private static func appIconImage() -> UIImage {
+        if let icons = Bundle.main.object(forInfoDictionaryKey: "CFBundleIcons") as? [String: Any],
+           let primary = icons["CFBundlePrimaryIcon"] as? [String: Any],
+           let files = primary["CFBundleIconFiles"] as? [String],
+           let last = files.last,
+           let icon = UIImage(named: last) {
+            return icon
+        }
+        if let icon = UIImage(named: "AppIcon") { return icon }
+        let renderer = UIGraphicsImageRenderer(size: CGSize(width: 1, height: 1))
+        return renderer.image { _ in }
+    }
+
     // MARK: - URL / Base64 编码
 
     /// RFC 3986 unreserved + URL-encode（与 msext line 1262-1268 等价）