fix(audio): a cancelled announcement really stops; oto's Close is a no-op

Clicking Cancel reached the daemon and the queue cancelled the item, but
the sound played on to the end: oto v3's Player.Close only relies on the
garbage collector's finalizer, so the player stayed in the mix. Pause takes
it out immediately; only the device buffer (about 100 ms) drains. Same fix
covers talk cancel and daemon shutdown.

Direct speech via spd-say: killing the waiting client did not stop
speech-dispatcher either; on cancel it now sends `spd-say -S`.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/provider/osbuiltin.go

@@ -122,6 +122,12 @@ func (p OSBuiltin) SpeakDirect(ctx context.Context, text, lang string) error {
 		}
 		cmd := exec.CommandContext(ctx, "spd-say", "-w", "-l", lang, text)
 		if out, err := cmd.CombinedOutput(); err != nil {
+			if ctx.Err() != nil {
+				// Cancelled: killing the waiting client does not stop
+				// speech-dispatcher's output; tell it to stop explicitly.
+				_ = exec.Command("spd-say", "-S").Run()
+				return ctx.Err()
+			}
 			return fmt.Errorf("osbuiltin: spd-say failed: %w: %s", err, bytes.TrimSpace(out))
 		}
 		return nil