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/api.ts

@@ -12,6 +12,7 @@ import type {
   Quality,
   RefreshProgress,
   RefreshSummary,
+  Stream,
 } from "./types";
 
 export const checkPrereqs = () => invoke<Prereqs>("check_prereqs");
@@ -37,9 +38,19 @@ export const deleteDownload = (videoId: string) =>
 
 export const getConnectivity = () => invoke<boolean>("get_connectivity");
 
-/** A directly playable URL (HLS master playlist) for an undownloaded video. */
-export const resolveStream = (videoId: string) =>
-  invoke<string>("resolve_stream", { videoId });
+/**
+ * A directly playable URL for an undownloaded video. When a quality cap is set
+ * the backend serves a rewritten playlist from its own loopback server, so this
+ * is always a plain URL either way.
+ */
+export async function resolveStream(
+  videoId: string,
+  maxHeight: number | null,
+): Promise<string> {
+  const s = await invoke<Stream>("resolve_stream", { videoId, maxHeight });
+  if (!s.url) throw new Error("No playable stream was returned.");
+  return s.url;
+}
 
 export const setLibraryPath = (path: string) =>
   invoke<string>("set_library_path", { path });