feat(antigravity): 对齐 AM 客户端标识，前端 OAuth 增加 TOTP 支持

- User-Agent 改为 Electron 浏览器格式，新增 x-client-name/x-client-version/x-vscode-sessionid/x-goog-api-client header
- 移除 MODEL_ALIAS_MAP 别名映射，改为仅剥离 -online 后缀
- thinking 自动注入关键字新增 gemini-3.1-pro
- 新增定时 Antigravity UA 版本刷新任务（每 6 小时 + 启动时）
- 前端 OAuth 设备授权新增 TOTP 验证码生成（otpauth），Region 改为按钮选择
- SSO OIDC 轮询日志 authorization_pending/slow_down 降级为 debug

src/api/handlers/base/handler_adapter_base.py

@@ -371,9 +371,7 @@ class HandlerAdapterBase(ApiAdapter):
         elif is_antigravity:
             from src.services.provider.adapters.antigravity.constants import (
                 V1INTERNAL_PATH_TEMPLATE,
-            )
-            from src.services.provider.adapters.antigravity.constants import (
-                get_http_user_agent as _get_antigravity_ua,
+                get_v1internal_extra_headers,
             )
             from src.services.provider.adapters.antigravity.url_availability import (
                 url_availability,
@@ -392,7 +390,7 @@ class HandlerAdapterBase(ApiAdapter):
         merged_extra.update(cli_extra)
 
         if is_antigravity:
-            merged_extra["User-Agent"] = _get_antigravity_ua()
+            merged_extra.update(get_v1internal_extra_headers())
 
         if is_kiro:
             from src.services.provider.adapters.kiro.headers import (

src/api/handlers/gemini/adapter.py

@@ -297,9 +297,7 @@ class GeminiChatAdapter(ChatAdapterBase):
         if is_antigravity:
             from src.services.provider.adapters.antigravity.constants import (
                 V1INTERNAL_PATH_TEMPLATE,
-            )
-            from src.services.provider.adapters.antigravity.constants import (
-                get_http_user_agent as _get_antigravity_ua,
+                get_v1internal_extra_headers,
             )
             from src.services.provider.adapters.antigravity.url_availability import url_availability
 
@@ -316,7 +314,7 @@ class GeminiChatAdapter(ChatAdapterBase):
         # Antigravity 需要特定的 User-Agent
         merged_extra = dict(extra_headers) if extra_headers else {}
         if is_antigravity:
-            merged_extra["User-Agent"] = _get_antigravity_ua()
+            merged_extra.update(get_v1internal_extra_headers())
         headers = cls.build_headers_with_extra(api_key, merged_extra if merged_extra else None)
 
         # OAuth 统一处理：替换端点默认认证头（x-goog-api-key）为 Authorization: Bearer