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/package.json

@@ -18,28 +18,28 @@
     "test:unit:watch": "vitest"
   },
   "devDependencies": {
-    "@eslint/js": "^9.17.0",
-    "@sveltejs/adapter-static": "^3.0.6",
-    "@sveltejs/kit": "^2.15.0",
-    "@sveltejs/vite-plugin-svelte": "^5.0.3",
-    "@testing-library/jest-dom": "^6.6.3",
-    "@testing-library/svelte": "^5.2.6",
-    "@types/node": "^22.19.21",
-    "eslint": "^9.17.0",
-    "eslint-config-prettier": "^9.1.0",
-    "eslint-plugin-svelte": "^2.46.1",
-    "globals": "^15.14.0",
-    "jsdom": "^25.0.1",
-    "postcss-html": "^1.7.0",
-    "prettier": "^3.4.2",
-    "prettier-plugin-svelte": "^3.3.2",
-    "stylelint": "^16.12.0",
-    "stylelint-config-standard": "^36.0.1",
-    "svelte": "^5.16.0",
-    "svelte-check": "^4.1.1",
-    "typescript": "^5.7.2",
-    "typescript-eslint": "^8.18.2",
-    "vite": "^6.0.6",
-    "vitest": "^3.2.4"
+    "@eslint/js": "^10.0.1",
+    "@sveltejs/adapter-static": "^3.0.10",
+    "@sveltejs/kit": "^2.66.0",
+    "@sveltejs/vite-plugin-svelte": "^5.1.1",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/svelte": "^5.4.0",
+    "@types/node": "^26.0.0",
+    "eslint": "^10.5.0",
+    "eslint-config-prettier": "^10.1.8",
+    "eslint-plugin-svelte": "^3.19.0",
+    "globals": "^17.6.0",
+    "jsdom": "^29.1.1",
+    "postcss-html": "^1.8.1",
+    "prettier": "^3.8.4",
+    "prettier-plugin-svelte": "^4.1.1",
+    "stylelint": "^17.13.0",
+    "stylelint-config-standard": "^40.0.0",
+    "svelte": "^5.56.3",
+    "svelte-check": "^4.6.0",
+    "typescript": "^6.0.3",
+    "typescript-eslint": "^8.61.1",
+    "vite": "^6.4.3",
+    "vitest": "^4.1.9"
   }
 }