chore: clean svelte-check warnings (CSS, a11y, types)

Drains the wiki "23 warnings" baseline back to zero so future regressions
stand out:

* Drop 16 unprefixed \`app-region\` CSS lines across TitleBar, TitleBarNav,
  ImmersiveHeader, ImmersivePlayer, MiniPlayerFooter and MiniPlayerWindowControls.
  Tauri's webview is WebKit / Chromium on every platform we ship to, so
  \`-webkit-app-region\` already covers the chrome-drag region; the
  unprefixed property only existed to keep stylelint quiet but the CSS
  spec doesn't define it and svelte-check warns on every site.
* Remove 2 empty rulesets in AlbumCreditsModal and NowPlayingBar (leftover
  comment-only blocks from earlier refactors).
* Pair \`-moz-appearance: textfield\` with the standard \`appearance: textfield\`
  in LocalLibraryTagEditorModal so the rule no longer trips the
  property-companion warning.
* Delete the unused \`.quality-text\` selector in NowPlayingBar.backup.svelte
  (file is a frozen snapshot of an older NPB iteration; the live NPB
  doesn't use that class).
* Annotate Tooltip.svelte and immersive/panels/VinylPanel.svelte with
  \`svelte-ignore a11y_no_static_element_interactions\` plus a comment
  explaining the context — both are decorative wrappers (a tooltip hit
  area; a 3D tilt effect on artwork) where adding an ARIA role would
  misrepresent the semantics.
* Add \`@types/node\` as a devDependency (^22) so the tsconfig resolution
  for the SvelteKit-extended config stops complaining about the missing
  type definition.

cc

package.json

@@ -45,6 +45,7 @@
     "@sveltejs/vite-plugin-svelte": "^7.0.0",
     "@tauri-apps/cli": "^2",
     "@testing-library/svelte": "^5.3.1",
+    "@types/node": "^22.19.18",
     "jsdom": "^29.1.1",
     "svelte": "^5.55.5",
     "svelte-check": "^4.4.8",