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/SessionDropdown.tsx

@@ -4,8 +4,7 @@
 import { Component, createSignal, For, Show } from "solid-js";
 import {
   sessions,
-  setSessionId,
-  hydrateFromServer,
+  joinSession,
   useJournalStream,
 } from "../stores/journalStream";
 
@@ -25,8 +24,9 @@ export const SessionDropdown: Component<SessionDropdownProps> = (props) => {
       return;
     }
     setDropdownOpen(false);
-    setSessionId(id);
-    hydrateFromServer(id).catch(() => {});
+    joinSession(id).catch((e) => {
+      console.error("[journal] failed to switch session:", e);
+    });
   };
 
   // Close dropdown on outside click