fix: private chat creation and search in NewChatModal

- Fix: onOpen now async, MainLayout fetches fresh chats before opening
  (was using stale closure, chat wasn't found after creation)
- Fix: search null-safety in user list filter (displayName/username could be undefined)
- Fix: search also matches by phone number

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/MainLayout.tsx

@@ -246,9 +246,13 @@ export default function MainLayout() {
       </div>
 
       {/* Modals */}
-      {showNew && <NewChatModal onClose={() => setShowNew(false)} onOpen={(id) => {
-        const chat = chats.find(c => c.id === id);
-        if (chat) openChat(chat);
+      {showNew && <NewChatModal onClose={() => setShowNew(false)} onOpen={async (id) => {
+        try {
+          const { data: allChats } = await api.get('/api/chats');
+          setChats(allChats);
+          const found = allChats.find((c: any) => c.id === id);
+          if (found) openChat(found);
+        } catch {}
       }} />}
       {showAdmin && <AdminPanel onClose={() => setShowAdmin(false)} />}
       {showProfile && <ProfileModal onClose={() => setShowProfile(false)} />}