(restore): save the open sessions when the app closes, last review round (#479) - #555

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

'bgAgentSessionIds' is already defined as a built-in global variable

'wireActivityTraceToggle' is already defined as a built-in global variable

'renderActivityTraceFiles' is already defined as a built-in global variable

'openActivityTraceFile' is already defined as a built-in global variable

'diffId' is assigned a value but never used. Allowed unused vars must match /^_/u

'useWslProfile' is assigned a value but never used. Allowed unused vars must match /^_/u

'sendStatus' is assigned a value but never used. Allowed unused vars must match /^_/u

'readFolderFromFilesystem' is assigned a value but never used. Allowed unused vars must match /^_/u

'readSessionFile' is assigned a value but never used. Allowed unused vars must match /^_/u

'discoverShellProfiles' is assigned a value but never used. Allowed unused vars must match /^_/u