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/CreateSessionDialog.tsx

@@ -2,7 +2,7 @@
  * CreateSessionDialog — modal for naming a new session
  */
 import { Component, createSignal, onMount } from "solid-js";
-import { createSession, setSessionId, hydrateFromServer } from "../stores/journalStream";
+import { createSession, joinSession } from "../stores/journalStream";
 
 interface CreateSessionDialogProps {
   onClose: () => void;
@@ -19,15 +19,16 @@ export const CreateSessionDialog: Component<CreateSessionDialogProps> = (
     const trimmed = name().trim();
     if (!trimmed) return;
     setCreating(true);
-    const id = createSession(trimmed);
-    if (id) {
-      setSessionId(id);
-      // Hydrate the new (empty) session so the UI reflects it immediately
-      await hydrateFromServer(id).catch(() => {});
+    try {
+      const id = await createSession(trimmed);
+      if (id) await joinSession(id);
+    } catch (e) {
+      console.error("[journal] failed to create session:", e);
+    } finally {
+      setName("");
+      setCreating(false);
+      props.onClose();
     }
-    setName("");
-    setCreating(false);
-    props.onClose();
   };
 
   onMount(() => inputRef?.focus());