feat(s2a_service): Add pure API authorization mode without browser

- Add S2A_API_MODE configuration option to enable browser-less authorization
- Implement S2AApiAuthorizer class using curl_cffi for browser fingerprint simulation
- Add Sentinel PoW (Proof of Work) solver with FNV-1a hashing algorithm
- Implement OAuth flow via direct API calls instead of browser automation
- Add s2a_api_authorize() function to handle email/password authentication
- Support proxy configuration for API requests
- Add requirements token generation for API authentication
- Update browser_automation.py to check S2A_API_MODE and route to API or browser flow
- Update config.py to load S2A_API_MODE from configuration
- Add api_mode option to config.toml.example with documentation
- Improves performance and stability by eliminating browser overhead while maintaining compatibility with existing browser-based flow

config.toml.example

@@ -154,6 +154,11 @@ priority = 50
 group_ids = []
 # 分组名称列表 (优先使用 group_ids，如果未配置则通过名称查询 ID)
 group_names = []
+# 是否使用纯 API 授权模式 (无需浏览器)
+# 开启后使用 curl_cffi 直接调用 OpenAI 认证 API 完成授权
+# 优点: 更快、更稳定、无需浏览器
+# 缺点: 需要安装 curl_cffi (pip install curl_cffi)
+api_mode = false
 
 # ==================== 账号配置 ====================
 [account]