feat: uniform control height, chrome auto-hide, streaming quality

Every control in the app now shares one height (CONTROL_H), with width
still growing to fit its label. The player transport is larger, Back is
an icon, and the footer buttons match the prev/next size.

Player chrome — transport and edge arrows — fades after 2.6s of
inactivity and never hides while paused.

The title-bar strip collapses in macOS window fullscreen, where the
traffic lights are gone and it was just a blank white bar.

Streaming quality is now selectable alongside download quality. A cap is
applied by rewriting YouTube's HLS master playlist down to the best
variant at or below the chosen height, keeping its audio group. That
playlist is served from a small loopback HTTP server: Safari's native
HLS is backed by AVFoundation, which cannot read blob: or custom-scheme
URLs, so a Blob URL silently fails to play.

Settings closes with an icon button and its selects match the shared
control height.

src/hooks/useWindowFullscreen.ts

@@ -0,0 +1,24 @@
+import { getCurrentWindow } from "@tauri-apps/api/window";
+import { useEffect, useState } from "react";
+
+/**
+ * True while the macOS *window* is fullscreen (the green button), as distinct
+ * from the video being fullscreen. In that state the traffic lights are gone,
+ * so the title-bar strip the app paints is pure dead space and must collapse.
+ */
+export function useWindowFullscreen(): boolean {
+  const [full, setFull] = useState(false);
+
+  useEffect(() => {
+    const win = getCurrentWindow();
+    let unlisten: (() => void) | undefined;
+    const check = () => {
+      win.isFullscreen().then(setFull).catch(() => {});
+    };
+    check();
+    win.onResized(check).then((u) => (unlisten = u));
+    return () => unlisten?.();
+  }, []);
+
+  return full;
+}