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-tauri/Cargo.toml

@@ -31,3 +31,6 @@ futures = "0.3.34"
 tauri-plugin-dialog = "2.7.2"
 reqwest = { version = "0.13.4", default-features = false, features = ["rustls", "http2", "charset", "stream", "gzip"] }
 
+[target.'cfg(target_os = "macos")'.dependencies]
+objc2-web-kit = { version = "0.3.2", features = ["WKWebView", "WKWebViewConfiguration", "WKPreferences"] }
+