feat: subtitles, delete-all, auto refresh, and menu cleanup

Subtitles: a language preference in Settings drives what is shown and
what is downloaded. yt-dlp saves WebVTT sidecars next to each download,
including YouTube's auto-generated track, and the player attaches them
as <track> elements so they work offline. Sidecars are removed with
their video, and by Delete all.

WebVTT rather than muxed subtitle streams because WebKit reads a <track>
reliably and largely ignores subtitle tracks inside an MP4.

Downloads in progress now appear under the downloaded-only filter, so a
download you just started does not vanish from the list you are watching
it in. That view also gains a Delete all, behind a confirmation naming
what goes.

The feed refreshes on launch and whenever the player closes, so the
Refresh button is only for staleness.

Player: Delete moved to the footer and shortened, Open on YouTube is now
an external-link icon.

Removes the Edit and Help menus. Cut/Copy/Paste move to the app menu,
without which their shortcuts would stop working in the search field.
The webview context menu is suppressed outside text fields — its Reload
and Back items act on a page the app does not present as one.

Settings now warns that 4K AV1 plays back with artefacts: the files
decode cleanly in ffmpeg, so it is the built-in decoder, not the
download.

src/components/Settings.tsx

@@ -4,7 +4,8 @@ import {
 } from "../api";
 import { APPEARANCE_MODES, type Appearance } from "../hooks/useAppearance";
 import {
-  QUALITIES, STREAM_QUALITIES, type ImportPreview, type Prereqs, type Quality,
+  QUALITIES, STREAM_QUALITIES, SUB_LANGS,
+  type ImportPreview, type Prereqs, type Quality,
 } from "../types";
 import TakeoutGuide from "./TakeoutGuide";
 import {
@@ -20,6 +21,8 @@ interface Props {
   onQuality: (q: Quality) => void;
   streamQuality: Quality;
   onStreamQuality: (q: Quality) => void;
+  subLang: string;
+  onSubLang: (l: string) => void;
   onError: (message: string) => void;
 }
 
@@ -44,7 +47,7 @@ function StatusRow({ label, value }: { label: string; value: string | null }) {
 
 export default function Settings({
   onClose, onImported, appearance, onAppearance, quality, onQuality,
-  streamQuality, onStreamQuality, onError,
+  streamQuality, onStreamQuality, subLang, onSubLang, onError,
 }: Props) {
   const [prereqs, setPrereqs] = useState<Prereqs | null>(null);
   const [pending, setPending] = useState<{ path: string; preview: ImportPreview } | null>(null);
@@ -182,6 +185,26 @@ export default function Settings({
                 Streaming quality applies when you play something you have not downloaded.
                 Best lets the player adapt to your connection; a fixed height pins it.
               </p>
+
+              <label className="mt-3 grid grid-cols-[92px_1fr] items-center gap-2">
+                <span className={LABEL}>Subtitles</span>
+                <select
+                  value={subLang}
+                  onChange={(e) => onSubLang(e.target.value)}
+                  className={SELECT}
+                >
+                  {SUB_LANGS.map((l) => (
+                    <option key={l.value} value={l.value}>
+                      {l.label}
+                    </option>
+                  ))}
+                </select>
+              </label>
+              <p className={`mt-2 ${HELP}`}>
+                Shown automatically when a video has subtitles in this language, including
+                YouTube's auto-generated ones, and saved alongside anything you download so
+                they work offline. You can still switch tracks from the player.
+              </p>
             </section>
 
             <section className="border-b border-slate-200 px-5 py-4 dark:border-slate-800">