feat(tts): add method selector (speaker | radio) to TTS speak

/setup/tts/speak now accepts a "method" field (and the CLI a --method
flag): "radio" (default, LOCAL_INTERNET_RADIO, no app_key, replaces
source) or "speaker" (POST /speaker notification, ducks+resumes, honours
volume). The speaker method defaults the app_key to "aftertouch" when
none is configured, since the speaker validates it via GET /v1/auth which
we answer 200 regardless.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/soundtouch-cli/cmd_tts.go

@@ -63,7 +63,12 @@ func ttsSpeakCmd() *cli.Command {
 			&cli.IntFlag{
 				Name:    "volume",
 				Aliases: []string{"v"},
-				Usage:   "Playback volume (0-100, 0 = service default)",
+				Usage:   "Playback volume (0-100, 0 = service default; only honoured by --method speaker)",
+			},
+			&cli.StringFlag{
+				Name:  "method",
+				Usage: "Playback method: 'radio' (LOCAL_INTERNET_RADIO, no app_key, replaces source) or 'speaker' (/speaker notification, ducks+resumes, supports volume)",
+				Value: "radio",
 			},
 		),
 		Action: ttsSpeak,
@@ -100,6 +105,10 @@ func ttsSpeak(c *cli.Context) error {
 		payload["volume"] = c.Int("volume")
 	}
 
+	if m := c.String("method"); m != "" {
+		payload["method"] = m
+	}
+
 	body, err := json.Marshal(payload)
 	if err != nil {
 		return fmt.Errorf("marshal request: %w", err)