feat(download): 添加快手下载器并优化下载配置功能

- 新增快手下载器，支持快手视频下载
- 添加下载配置页面，可设置各平台Cookies
- 优化后端接口，增加获取和更新Cookies的功能
- 前端新增Downloader组件和相关表单组件
- 更新路由配置，增加下载配置相关路由

backend/app/services/constant.py

@@ -1,5 +1,6 @@
 from app.downloaders.bilibili_downloader import BilibiliDownloader
 from app.downloaders.douyin_downloader import DouyinDownloader
+from app.downloaders.kuaishou_downloader import KuaiShouDownloader
 from app.downloaders.local_downloader import LocalDownloader
 from app.downloaders.youtube_downloader import YoutubeDownloader
 
@@ -7,6 +8,7 @@ SUPPORT_PLATFORM_MAP = {
     'youtube':YoutubeDownloader(),
     'bilibili':BilibiliDownloader(),
     'tiktok':DouyinDownloader(),
+    'kuaishou':KuaiShouDownloader(),
     'douyin':DouyinDownloader(),
     'local':LocalDownloader()
 }

backend/app/services/cookie_manager.py

@@ -0,0 +1,44 @@
+import json
+from pathlib import Path
+from typing import Optional, Dict
+
+
+class CookieConfigManager:
+    def __init__(self, filepath: str = "config/downloader.json"):
+        self.path = Path(filepath)
+        self.path.parent.mkdir(parents=True, exist_ok=True)
+        if not self.path.exists():
+            self._write({})
+
+    def _read(self) -> Dict[str, Dict[str, str]]:
+        try:
+            with self.path.open("r", encoding="utf-8") as f:
+                return json.load(f)
+        except Exception:
+            return {}
+
+    def _write(self, data: Dict[str, Dict[str, str]]):
+        with self.path.open("w", encoding="utf-8") as f:
+            json.dump(data, f, ensure_ascii=False, indent=2)
+
+    def get(self, platform: str) -> Optional[str]:
+        data = self._read()
+        return data.get(platform, {}).get("cookie")
+
+    def set(self, platform: str, cookie: str):
+        data = self._read()
+        data[platform] = {"cookie": cookie}
+        self._write(data)
+
+    def delete(self, platform: str):
+        data = self._read()
+        if platform in data:
+            del data[platform]
+            self._write(data)
+
+    def list_all(self) -> Dict[str, str]:
+        data = self._read()
+        return {k: v.get("cookie", "") for k, v in data.items()}
+
+    def exists(self, platform: str) -> bool:
+        return self.get(platform) is not None