feat: 支持x-login-as三参数认证、auth_url跟随base_url

- 认证请求增加x-login-as header支持连接账户
- auth_url根据base_url动态构建，不再硬编码生产环境
- 默认Base URL改为demo环境
- 设置页面新增Account ID字段，带tooltip说明

backend/app/proxy_client.py

@@ -2,16 +2,20 @@
 import logging
 import httpx
 from datetime import datetime, timezone, timedelta
+from typing import Optional
 from airwallex.client import AirwallexClient
 
 logger = logging.getLogger(__name__)
 
 
 class ProxiedAirwallexClient(AirwallexClient):
-    """AirwallexClient that routes requests through an HTTP or SOCKS5 proxy."""
+    """AirwallexClient that routes requests through an HTTP or SOCKS5 proxy.
+    Also supports x-login-as header for connected accounts.
+    """
 
-    def __init__(self, proxy_url: str | None = None, **kwargs):
+    def __init__(self, proxy_url: str | None = None, login_as: str | None = None, **kwargs):
         self._proxy_url = proxy_url
+        self._login_as = login_as
         super().__init__(**kwargs)
         # Replace the default httpx client with a proxied one
         if proxy_url:
@@ -27,26 +31,30 @@ class ProxiedAirwallexClient(AirwallexClient):
             logger.info("Airwallex client initialized without proxy")
 
     def authenticate(self) -> None:
-        """Override authenticate to use proxy for auth requests too."""
+        """Override authenticate to use proxy and x-login-as for auth requests."""
         if self._token and self._token_expiry and datetime.now(timezone.utc) < self._token_expiry:
             return
 
-        logger.info("Authenticating with Airwallex API at %s (proxy: %s)",
-                     self.auth_url, bool(self._proxy_url))
+        logger.info("Authenticating with Airwallex API at %s (proxy: %s, login_as: %s)",
+                     self.auth_url, bool(self._proxy_url), self._login_as or "none")
 
         auth_kwargs: dict = {"timeout": self.request_timeout}
         if self._proxy_url:
             auth_kwargs["proxy"] = self._proxy_url
 
+        auth_headers = {
+            "Content-Type": "application/json",
+            "x-client-id": self.client_id,
+            "x-api-key": self.api_key,
+        }
+        if self._login_as:
+            auth_headers["x-login-as"] = self._login_as
+
         auth_client = httpx.Client(**auth_kwargs)
         try:
             response = auth_client.post(
                 self.auth_url,
-                headers={
-                    "Content-Type": "application/json",
-                    "x-client-id": self.client_id,
-                    "x-api-key": self.api_key,
-                },
+                headers=auth_headers,
                 content="{}",
             )
 
@@ -61,3 +69,11 @@ class ProxiedAirwallexClient(AirwallexClient):
             logger.info("Authentication successful, token expires in 28 minutes")
         finally:
             auth_client.close()
+
+    @property
+    def headers(self):
+        """Add x-login-as to all API request headers."""
+        h = super().headers
+        if self._login_as:
+            h["x-login-as"] = self._login_as
+        return h