Add set_basic_auth and set_bearer_token_auth to WebSocketClient (#2652)

ClientImpl and SSLClient let callers set origin credentials with
set_basic_auth()/set_bearer_token_auth(), but WebSocketClient could only
take a fixed Authorization header through its constructor. Add both
setters: each connect() adds the Authorization header to the upgrade
request from the current credentials (Basic over Bearer), unless the
constructor headers already carry one, and never to the proxy's CONNECT
request.

README-websocket.md

@@ -200,6 +200,10 @@ void close(CloseStatus status = CloseStatus::Normal,
            const std::string &reason = "");
 bool is_open() const;
 
+// Authentication - the same setters Client has (Basic wins over Bearer).
+void set_basic_auth(const std::string &username, const std::string &password);
+void set_bearer_token_auth(const std::string &token);
+
 // Proxy - the same setters Client has. connect() opens a CONNECT tunnel
 // through the proxy for ws:// as well as wss:// (RFC 6455 4.1); the proxy
 // credentials are sent only on the CONNECT request, never through the tunnel.
@@ -404,6 +408,22 @@ svr.set_pre_request_handler([](const httplib::Request &req, httplib::Response &r
 
 The server accepts a handshake from any `Origin`. A browser sends its cookies with a handshake another site starts, so if cookies authenticate the connection, also check `req.get_header_value("Origin")` against your own origins in one of these handlers (cross-site WebSocket hijacking).
 
+### Authentication
+
+```cpp
+httplib::ws::WebSocketClient ws("wss://example.com/ws");
+ws.set_bearer_token_auth("token123");      // Authorization: Bearer token123
+// or
+ws.set_basic_auth("user", "pass");         // Authorization: Basic dXNlcjpwYXNz
+
+if (ws.connect()) { /* ... */ }
+```
+
+The credentials are read on every `connect()`, so a new token takes effect on
+the next reconnect. An `Authorization` header passed to the constructor wins
+over them. Through a proxy they are sent only inside the tunnel, never on
+`CONNECT`.
+
 ### Custom Headers and Timeouts
 
 ```cpp