feat(ui): scale the whole window with Interface Scale (#781)

* experiment(zoom): allow setting webview zoom via core capability

* experiment(zoom): drive uiScale through Tauri's native webview zoom

Replace the CSS `zoom: uiScale` on `.main-content-zoom` (which only
scaled the main content column, leaving the sidebar, queue panel,
player bar and portaled overlays at 1.0) with a `setZoom` call on the
current webview. That scales everything inside the window the same way
Ctrl+/− does in a browser, including portals and the queue panel.

Effect runs whenever `uiScale` changes and once on mount, so the
persisted setting is reapplied on launch.

* docs: changelog + credits for interface scale (#781)

src-tauri/capabilities/default.json

@@ -38,6 +38,7 @@
     "core:window:allow-create",
     "core:window:allow-set-size",
     "core:webview:allow-create-webview-window",
+    "core:webview:allow-set-webview-zoom",
     "process:allow-restart",
     "updater:default"
   ]