fix: native video fullscreen, window dragging, quality picker, spinner

Enable WKWebView's elementFullscreenEnabled at startup. It is off by
default in a Tauri window, which is why the native player had no
full-screen button and why right-click 'Enter Full Screen' did nothing.
With it on, WebKit's own control appears on the video and gives the real
system fullscreen player, so the app-level workaround is gone.

Restore window dragging: data-tauri-drag-region needs
core:window:allow-start-dragging, which was missing, leaving the
title-bar strip inert.

Download quality is now a resolution picker (best/2160/1440/1080/720/
480) instead of a two-way toggle; every selector still pins AAC audio
because Opus in MP4 is silent in WebKit.

Tile titles truncate to a single line so rows stay uniform, and the
player shows a spinner while the video buffers, not just while the
stream URL resolves.

src/App.tsx

@@ -13,7 +13,7 @@ import { useAppearance } from "./hooks/useAppearance";
 import { useConnectivity } from "./hooks/useConnectivity";
 import { useDownloads } from "./hooks/useDownloads";
 import { useFeed } from "./hooks/useFeed";
-import type { FeedFilter, FeedItem, Quality, RefreshProgress } from "./types";
+import { QUALITIES, type FeedFilter, type FeedItem, type Quality, type RefreshProgress } from "./types";
 
 const TOAST_MS = 2400;
 
@@ -34,9 +34,8 @@ export default function App() {
   const [playingIndex, setPlayingIndex] = useState<number | null>(null);
   const [quality, setQuality] = useState<Quality>(() => {
     try {
-      return localStorage.getItem("flighttube.quality") === "compatible"
-        ? "compatible"
-        : "best";
+      const stored = localStorage.getItem("flighttube.quality");
+      return QUALITIES.some((q) => q.value === stored) ? (stored as Quality) : "best";
     } catch {
       return "best";
     }