(fix): session id stuff

README.md

@@ -64,10 +64,14 @@ let client = TAuthClient::new(
 
 ## Start Login
 
-Redirect the user to `client.auth_url(None)` from your web handler.
+Redirect the user to `client.auth_url(None, session_id)` from your web handler. The `session_id` is a `u64` you generate (e.g. from the current time in milliseconds) — it is passed through the TAuth flow and returned in the callback so you can correlate the login with a pending session.
 
 ```rust
-let login_url = client.auth_url(None);
+let session_id = std::time::SystemTime::now()
+    .duration_since(std::time::UNIX_EPOCH)
+    .map(|d| d.as_millis() as u64)
+    .unwrap_or(0);
+let login_url = client.auth_url(None, session_id);
 ```
 
 The URL includes:
@@ -75,6 +79,7 @@ The URL includes:
 - `identifier`: your app identifier
 - `redirect`: your callback URL
 - `public_key`: your app MTP public key bundle
+- `sessionId`: the session ID you generated, passed through to the callback
 - `challenge`: optional caller-supplied challenge
 
 ## Handle Callback