fix(realtime): eliminate cpu reconnect loop, singleton global connection & fix disappearing notes

frontend/src/App.tsx

@@ -1,4 +1,4 @@
-import React, { useEffect, useRef, useState } from 'react';
+import React, { useCallback, useEffect, useRef, useState } from 'react';
 import {
   Layers,
   CheckSquare,
@@ -414,7 +414,7 @@ export const App: React.FC = () => {
     setActiveThemeState(themeId);
   };
 
-  const refreshAll = async () => {
+  const refreshAll = useCallback(async () => {
     try {
       const [meRes, deckRes, listsRes] = await Promise.all([
         api.getMe(),
@@ -428,7 +428,7 @@ export const App: React.FC = () => {
     } catch {
       // If token expired or invalid, api.ts dispatches mindsift:unauthorized
     }
-  };
+  }, []);
 
   const checkBootAndAuth = async () => {
     setBootLoading(true);