feat: add client support for proxy authentication

- Add MCP_PROXY_AUTH_TOKEN configuration field to store session token
- Update useConnection hook to include proxy auth token in all requests
- Add separate proxy auth headers to avoid conflicts with MCP server auth
- Add specific error handling for proxy authentication failures
- Show helpful toast message directing users to Configuration settings
- Update README with instructions for configuring token in UI

The client now properly authenticates with the proxy server using the
session token displayed in the proxy console.

client/src/utils/configUtils.ts

@@ -28,6 +28,10 @@ export const getMCPServerRequestMaxTotalTimeout = (
   return config.MCP_REQUEST_MAX_TOTAL_TIMEOUT.value as number;
 };
 
+export const getMCPProxyAuthToken = (config: InspectorConfig): string => {
+  return config.MCP_PROXY_AUTH_TOKEN.value as string;
+};
+
 const getSearchParam = (key: string): string | null => {
   try {
     const url = new URL(window.location.href);