fix(oauth): reqwest 启用 system-proxy；Google 换 token 诊断与 0.5.26

- 工作区 reqwest 增加 system-proxy，与系统代理一致
- google.rs：超时/非 2xx 体日志；OAuth 请求单独 45s 超时
- README / AGENTS / deploy/.env.example：OAuth 出站与 HTTPS_PROXY 说明

Cargo.toml

@@ -36,4 +36,5 @@ tracing-subscriber = { version = "^0.3", features = ["env-filter"] }
 dotenvy = "^0.15"
 
 # HTTP
-reqwest = { version = "^0.12", default-features = false, features = ["rustls-tls", "json"] }
+# system-proxy：与浏览器一致，读取 macOS/Windows 系统代理（禁用 default 后须显式开启，否则 OAuth 出站不走 Clash 等）
+reqwest = { version = "^0.12", default-features = false, features = ["rustls-tls", "json", "system-proxy"] }