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/journal/ConnectionBar.tsx

@@ -25,7 +25,11 @@ export const ConnectionBar: Component = () => {
   const handleCreateSession = () => {
     const name = newSessionName().trim();
     if (!name) return;
-    createSession(name);
+    const id = createSession(name);
+    if (id) {
+      setSessionId(id);
+      hydrateFromServer(id).catch(() => {});
+    }
     setNewSessionName("");
     setShowNewSession(false);
   };