feat: update session creation to hydrate data immediately

Update `createSession` to return the session ID, allowing the UI to
automatically set the active session and trigger a server hydration
immediately after creation. This ensures the UI reflects the new
session state without a manual refresh.

src/components/stores/journalStream.ts

@@ -370,8 +370,8 @@ export async function connectStream(
  * Create a new session by publishing retained metadata to its meta topic.
  * The server picks it up and adds it to the $SESSIONS manifest.
  */
-export function createSession(name: string, players: string[] = []): void {
-  if (!_mqttClient || !_mqttConnected) return;
+export function createSession(name: string, players: string[] = []): string | null {
+  if (!_mqttClient || !_mqttConnected) return null;
 
   const id =
     name
@@ -385,6 +385,8 @@ export function createSession(name: string, players: string[] = []): void {
     qos: 1,
     retain: true,
   });
+
+  return id;
 }
 
 /**