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.

vite.config.js

@@ -258,12 +258,12 @@ export default defineConfig({
     }),
   ],
   optimizeDeps: {
-    esbuildOptions: {
+    rolldownOptions: {
       define: {
         global: 'globalThis',
       },
       plugins: [
-        // Enable esbuild polyfill plugins
+        // Enable polyfill plugins
         NodeGlobalsPolyfillPlugin({
           process: false,
           buffer: true,
@@ -272,6 +272,7 @@ export default defineConfig({
     },
   },
   build: {
+    target: 'es2022',
     outDir: 'dist',
     sourcemap: true,
     copyPublicDir: false,