fix(journal): decouple broker from session

The broker connection now persists across session changes. Joining or switching a session swaps subscriptions instead of reconnecting, and a lobby lets sessions be listed and created before joining one.

Fixes session switching being a no-op (the store only updated local state) and session creation being unreachable before connecting. Also removes the dead ConnectionBar and the no-op hydrateFromServer/setSessionId store calls.

src/components/journal/index.ts

@@ -14,9 +14,12 @@ export {
 } from "./registry";
 export type { MessageTypeDef, StreamMessage } from "./registry";
 export {
-  connectStream,
+  connectBroker,
+  joinSession,
+  switchSession,
+  leaveSession,
   disconnectStream,
-  hydrateFromServer,
+  resolveBrokerUrl,
   sendMessage,
   revertLatest,
   canRevert,
@@ -42,7 +45,6 @@ export { ConnectDialog } from "./ConnectDialog";
 export { InviteDialog } from "./InviteDialog";
 export { SessionDropdown } from "./SessionDropdown";
 export { CreateSessionDialog } from "./CreateSessionDialog";
-export { ConnectionBar } from "./ConnectionBar";
 export { StreamView } from "./StreamView";
 export { StreamMessageCard } from "./StreamMessage";
 export { ComposePanel } from "./ComposePanel";