a11y: screen reader and keyboard improvements

- Audio player: aria-labels for Play/Pause, Loop, Mute, Close; labelled playback and volume sliders
- Generation: aria-labels for Generate speech and Fine tune instructions buttons
- Voice cards: focusable, labelled, Enter/Space to select
- History rows: focusable, labelled, Enter/Space to play; transcript textarea labelled
- Voices tab: focusable rows, labelled, Enter/Space to edit; Actions button labelled
- Model management: focusable model rows and labelled Download/Delete buttons
- Server tab: regions with aria-label and tabIndex for Connection, Status, App Updates
- Stories: focusable story rows, labelled, Enter/Space to select; Actions and track editor buttons labelled
- Voice profile samples: Play/Pause/Stop and mini-player slider labelled

Tested with NVDA and Narrator on Windows. See docs/PR-ACCESSIBILITY.md for full description.

Made-with: Cursor

app/src/components/ServerSettings/ServerStatus.tsx

@@ -10,7 +10,11 @@ export function ServerStatus() {
   const serverUrl = useServerStore((state) => state.serverUrl);
 
   return (
-    <Card>
+    <Card
+      role="region"
+      aria-label="Server Status"
+      tabIndex={0}
+    >
       <CardHeader>
         <CardTitle>Server Status</CardTitle>
       </CardHeader>