feat: replace nansixian with sixian when input to tts model

app.py

@@ -80,6 +80,8 @@ def text_to_speech(
             f"句子中的[{','.join(missing_words)}]目前無法轉成 ipa。請嘗試其他句子。"
         )
     parsed_ipa = parse_ipa(ipa)
+    if dialect == "nansixian":
+        dialect = "sixian"
     if use_default_emb_or_custom == "預設語者":
         wav = _do_tts(
             model_id,