chore(frontend): toolchain migration checkpoint + UI perf optimizations

Checkpoint of the in-progress frontend toolchain work (Vite pinned to ^6 after
the 7/8 rolldown build break, eslint-plugin-svelte v3 navigation/reactivity
fixes, CI/Dockerfile/manifest updates) together with three UI performance
optimizations (verified on the Vite 6 build):

- Critical CSS: move auth.css/music.css off the global path into their route
  chunks (login/device/nextcloud-login, music) -- -25% gzipped critical CSS
  (~5.4 KB) on every non-auth/non-music page load.
- relativeTimeAgo: cache the Intl.RelativeTimeFormat (was rebuilt per call, once
  per row per render) -- 22.7x faster date formatting in large lists.
- Virtualize search results and grouped trash (list view) via VirtualList -- DOM
  rows mounted stay ~constant (~27) instead of O(N) (94.6% fewer for 500 hits).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/routes/shared-with-me/+page.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
 	import { errorMessage } from '$lib/utils/errors';
 	import { goto } from '$app/navigation';
+	import { resolve } from '$app/paths';
 	import { onMount } from 'svelte';
 	import { dateBucket, resolveOwnerName, typeLabel } from '$lib/api/endpoints/favorites';
 	import { fetchSharedWithMe, type IncomingGrantItem } from '$lib/api/endpoints/grants';
@@ -114,7 +115,7 @@
 
 	function open(entry: ResourceEntry) {
 		if (entry.kind === 'folder') {
-			goto(`/files/${entry.id}`);
+			goto(resolve(`/files/${entry.id}`));
 			return;
 		}
 		const item = byId.get(entry.id);