feat: add sherpa-onnx local TTS provider

Offline VITS TTS using sherpa-onnx, no network dependency.
Uses vits-melo-tts-zh_en model for Chinese/English.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/main/xiaozhi-server/core/providers/tts/sherpa_tts.py

@@ -0,0 +1,55 @@
+import io
+import wave
+import numpy as np
+import sherpa_onnx
+from config.logger import setup_logging
+from core.providers.tts.base import TTSProviderBase
+
+TAG = __name__
+logger = setup_logging()
+
+
+class TTSProvider(TTSProviderBase):
+    def __init__(self, config, delete_audio_file):
+        super().__init__(config, delete_audio_file)
+        model_dir = config.get("model_dir", "models/vits-melo-tts-zh_en")
+        speed = config.get("speed", 1.0)
+        self.speed = float(speed) if speed else 1.0
+        self.sid = int(config.get("sid", 0))
+
+        tts_config = sherpa_onnx.OfflineTtsConfig(
+            model=sherpa_onnx.OfflineTtsModelConfig(
+                vits=sherpa_onnx.OfflineTtsVitsModelConfig(
+                    model=f"{model_dir}/model.onnx",
+                    lexicon=f"{model_dir}/lexicon.txt",
+                    tokens=f"{model_dir}/tokens.txt",
+                    dict_dir=f"{model_dir}/dict",
+                ),
+            ),
+            rule_fsts=f"{model_dir}/date.fst,{model_dir}/phone.fst,{model_dir}/number.fst,{model_dir}/new_heteronym.fst",
+            max_num_sentences=1,
+        )
+        self.tts = sherpa_onnx.OfflineTts(tts_config)
+        self.sample_rate = self.tts.sample_rate
+        logger.bind(tag=TAG).info(
+            f"SherpaOnnxTTS 初始化完成: model_dir={model_dir}, sample_rate={self.sample_rate}, sid={self.sid}"
+        )
+
+    async def text_to_speak(self, text, output_file):
+        audio = self.tts.generate(text, sid=self.sid, speed=self.speed)
+        samples = np.array(audio.samples, dtype=np.float32)
+        pcm = (samples * 32767).astype(np.int16)
+
+        wav_io = io.BytesIO()
+        with wave.open(wav_io, "wb") as wf:
+            wf.setnchannels(1)
+            wf.setsampwidth(2)
+            wf.setframerate(self.sample_rate)
+            wf.writeframes(pcm.tobytes())
+        wav_data = wav_io.getvalue()
+
+        if output_file:
+            with open(output_file, "wb") as f:
+                f.write(wav_data)
+        else:
+            return wav_data