refactor: 将 HTML 下载器拆分为子包结构

将 scripts/readers/html/downloader.py (263行) 拆分为 downloader/ 子包，各下载器独立维护：

- 创建 downloader/ 子包，包含 __init__.py、common.py 和 4 个下载器模块
- common.py 集中管理公共配置（USER_AGENT、CHROME_ARGS 等）
- 各下载器统一接口 download(url: str) -> Tuple[Optional[str], Optional[str]]
- 在 __init__.py 定义 DOWNLOADERS 列表显式注册，参考 parser 模式
- 更新 html/__init__.py 导入语句，从 .downloader import download_html
- 添加完整的类型注解，提升代码可维护性

scripts/readers/html/downloader/common.py

@@ -0,0 +1,65 @@
+"""下载器公共配置"""
+
+# 公共配置
+USER_AGENT = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36"
+WINDOW_SIZE = "1920,1080"
+LANGUAGE_SETTING = "zh-CN,zh"
+
+# Chrome 浏览器启动参数（pyppeteer 和 selenium 共用）
+CHROME_ARGS = [
+    "--no-sandbox",
+    "--disable-dev-shm-usage",
+    "--disable-gpu",
+    "--disable-software-rasterizer",
+    "--disable-extensions",
+    "--disable-background-networking",
+    "--disable-default-apps",
+    "--disable-sync",
+    "--disable-translate",
+    "--hide-scrollbars",
+    "--metrics-recording-only",
+    "--mute-audio",
+    "--no-first-run",
+    "--safebrowsing-disable-auto-update",
+    "--blink-settings=imagesEnabled=false",
+    "--disable-plugins",
+    "--disable-ipc-flooding-protection",
+    "--disable-renderer-backgrounding",
+    "--disable-background-timer-throttling",
+    "--disable-hang-monitor",
+    "--disable-prompt-on-repost",
+    "--disable-client-side-phishing-detection",
+    "--disable-component-update",
+    "--disable-domain-reliability",
+    "--disable-features=site-per-process",
+    "--disable-features=IsolateOrigins",
+    "--disable-features=VizDisplayCompositor",
+    "--disable-features=WebRTC",
+    f"--window-size={WINDOW_SIZE}",
+    f"--lang={LANGUAGE_SETTING}",
+    f"--user-agent={USER_AGENT}",
+]
+
+# 隐藏自动化特征的脚本（pyppeteer 和 selenium 共用）
+HIDE_AUTOMATION_SCRIPT = """
+    () => {
+        Object.defineProperty(navigator, 'webdriver', { get: () => undefined });
+        Object.defineProperty(navigator, 'plugins', { get: () => [1, 2, 3, 4, 5] });
+        Object.defineProperty(navigator, 'languages', { get: () => ['zh-CN', 'zh'] });
+    }
+"""
+
+# pyppeteer 额外的隐藏自动化脚本（包含 notifications 处理）
+HIDE_AUTOMATION_SCRIPT_PUPPETEER = """
+    () => {
+        Object.defineProperty(navigator, 'webdriver', { get: () => undefined });
+        Object.defineProperty(navigator, 'plugins', { get: () => [1, 2, 3, 4, 5] });
+        Object.defineProperty(navigator, 'languages', { get: () => ['zh-CN', 'zh'] });
+        const originalQuery = window.navigator.permissions.query;
+        window.navigator.permissions.query = (parameters) => (
+            parameters.name === 'notifications' ?
+                Promise.resolve({ state: Notification.permission }) :
+                originalQuery(parameters)
+        );
+    }
+"""