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/CreateSessionDialog.tsx

@@ -2,7 +2,7 @@
  * CreateSessionDialog — modal for naming a new session
  */
 import { Component, createSignal, onMount } from "solid-js";
-import { createSession } from "../stores/journalStream";
+import { createSession, setSessionId, hydrateFromServer } from "../stores/journalStream";
 
 interface CreateSessionDialogProps {
   onClose: () => void;
@@ -12,13 +12,21 @@ export const CreateSessionDialog: Component<CreateSessionDialogProps> = (
   props,
 ) => {
   const [name, setName] = createSignal("");
+  const [creating, setCreating] = createSignal(false);
   let inputRef!: HTMLInputElement;
 
-  const handleCreate = () => {
+  const handleCreate = async () => {
     const trimmed = name().trim();
     if (!trimmed) return;
-    createSession(trimmed);
+    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(() => {});
+    }
     setName("");
+    setCreating(false);
     props.onClose();
   };