feat(07-02): implement CookieManager class

- CookieManager saves cookies to ~/.kb_env file
- Updates existing ZHIHU_COOKIE line or appends new
- Preserves other configuration lines
- Sets file permissions to 600 for security
- Loads cookies from env file
- Clears get_settings cache after saving

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

kb_workflow/auth/cookie_manager.py

@@ -49,3 +49,72 @@ def parse_json_cookies(json_path: str) -> str:
                 zhihu_cookies.append(f"{name}={value}")
 
     return '; '.join(zhihu_cookies)
+
+
+class CookieManager:
+    """Cookie 持久化管理器
+
+    管理 Cookie 在 ~/.kb_env 文件中的存储和读取。
+    """
+
+    ENV_FILE_NAME = ".kb_env"
+    COOKIE_KEY = "ZHIHU_COOKIE"
+
+    def __init__(self, env_path: Path = None):
+        """初始化管理器
+
+        Args:
+            env_path: 环境文件路径，默认 ~/.kb_env
+        """
+        self.env_path = env_path or (Path.home() / self.ENV_FILE_NAME)
+
+    def save_cookie(self, cookie_str: str) -> None:
+        """保存 Cookie 到环境文件
+
+        格式: ZHIHU_COOKIE="name1=value1; name2=value2"
+
+        Args:
+            cookie_str: Cookie 字符串
+        """
+        # 读取现有内容
+        lines = []
+        if self.env_path.exists():
+            lines = self.env_path.read_text(encoding='utf-8').splitlines()
+
+        # 更新或添加 ZHIHU_COOKIE 行
+        cookie_line = f'{self.COOKIE_KEY}="{cookie_str}"'
+        found = False
+        for i, line in enumerate(lines):
+            if line.startswith(f"{self.COOKIE_KEY}="):
+                lines[i] = cookie_line
+                found = True
+                break
+        if not found:
+            lines.append(cookie_line)
+
+        # 写回文件，设置权限 600
+        self.env_path.write_text('\n'.join(lines) + '\n', encoding='utf-8')
+        self.env_path.chmod(0o600)
+
+        # 清除配置缓存
+        from kb_workflow.pipeline.config import get_settings
+        get_settings.cache_clear()
+
+    def load_cookie(self) -> str:
+        """从环境文件加载 Cookie
+
+        Returns:
+            Cookie 字符串，不存在时返回空字符串
+        """
+        if not self.env_path.exists():
+            return ""
+
+        content = self.env_path.read_text(encoding='utf-8')
+        for line in content.splitlines():
+            if line.startswith(f"{self.COOKIE_KEY}="):
+                # 提取引号内的值
+                value = line[len(f"{self.COOKIE_KEY}="):]
+                if value.startswith('"') and value.endswith('"'):
+                    value = value[1:-1]
+                return value
+        return ""