feat: upgrade toolchain and soften sync recovery after network blips

Bump Vite 8, matrix-js-sdk, and related deps; fix immer/vanilla-extract imports for new majors. Replace blocking sync error dialog with background recovery on wake/offline, and disable Vite auto-open in dev. Add feature handoff documentation index.

src/app/state/navToActivePath.ts

@@ -1,5 +1,5 @@
 import { WritableAtom, atom } from 'jotai';
-import produce from 'immer';
+import { produce } from 'immer';
 import { Path } from 'react-router-dom';
 import {
   atomWithLocalStorage,