feat: Whisper model selector + 16kHz mono recording

- App: AudioSamplingRateAndroid 16000 + AudioChannelsAndroid 1
  → Whisper bekommt direkt sein Ziel-Format, kein Resample mehr
- Bridge: STTEngine.reload() laedt Modell zur Laufzeit neu
  (tiny/base/small/medium/large-v3)
- Bridge: Config-Message triggert Hot-Reload wenn whisperModel sich aendert
- Bridge: Default auf 'medium' (besser als 'small' bei aehnlicher Latenz)
- Diagnostic: Neue Sektion "Whisper (Spracherkennung)" mit Dropdown,
  auto-save bei Auswahl, beim Laden wird der gespeicherte Wert gesetzt
- Diagnostic/Server: send_voice_config merged whisperModel in voice_config.json
- aria.env.example: WHISPER_MODEL + WHISPER_LANGUAGE dokumentiert

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

diagnostic/server.js

@@ -1253,7 +1253,11 @@ wss.on("connection", (ws) => {
         handleGetVoiceConfig(ws);
       } else if (msg.action === "send_voice_config") {
         // Stimmen-Config persistent speichern + an Bridge via RVS senden
+        // Bestehende Config lesen um Felder zu mergen die dieser Call nicht setzt
+        let existing = {};
+        try { existing = JSON.parse(fs.readFileSync("/shared/config/voice_config.json", "utf-8")); } catch {}
         const voiceConfig = {
+          ...existing,
           defaultVoice: msg.defaultVoice || "ramona",
           highlightVoice: msg.highlightVoice || "thorsten",
           ttsEnabled: msg.ttsEnabled !== false,
@@ -1262,12 +1266,13 @@ wss.on("connection", (ws) => {
           speedRamona: msg.speedRamona || 1.0,
           speedThorsten: msg.speedThorsten || 1.0,
         };
+        if (msg.whisperModel !== undefined) voiceConfig.whisperModel = msg.whisperModel;
         try {
           fs.mkdirSync("/shared/config", { recursive: true });
           fs.writeFileSync("/shared/config/voice_config.json", JSON.stringify(voiceConfig, null, 2));
         } catch {}
         sendToRVS_raw({ type: "config", payload: voiceConfig, timestamp: Date.now() });
-        log("info", "server", `Voice-Config gespeichert+gesendet: default=${voiceConfig.defaultVoice}, highlight=${voiceConfig.highlightVoice}, tts=${voiceConfig.ttsEnabled}`);
+        log("info", "server", `Voice-Config gespeichert+gesendet: default=${voiceConfig.defaultVoice}, whisper=${voiceConfig.whisperModel || "-"}`);
       } else if (msg.action === "get_triggers") {
         handleGetTriggers(ws);
       } else if (msg.action === "save_triggers") {