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/components/RouteTransition.tsx

@@ -1,20 +1,20 @@
 import React, { useEffect, useRef, useState } from 'react';
 import { useLocation } from 'react-router-dom';
-import { css } from '@vanilla-extract/css';
+import { style } from '@vanilla-extract/css';
 
-const transitionContainer = css({
+const transitionContainer = style({
   position: 'relative',
   width: '100%',
   height: '100%',
   overflow: 'hidden',
 });
 
-const transitionContent = css({
+const transitionContent = style({
   width: '100%',
   height: '100%',
 });
 
-const animateIn = css({
+const animateIn = style({
   animation: 'routeFadeSlideIn 0.25s cubic-bezier(0.4, 0, 0.2, 1)',
   '@keyframes': {
     routeFadeSlideIn: {
@@ -30,7 +30,7 @@ const animateIn = css({
   },
 });
 
-const animateOut = css({
+const animateOut = style({
   animation: 'routeFadeSlideOut 0.2s cubic-bezier(0.4, 0, 0.2, 1) forwards',
   '@keyframes': {
     routeFadeSlideOut: {