feat: add debug log control and optimize error response and cors log

- add DebugLog global variable controlled by BYTEDANCE_TTS_DEBUG env
- enable debug logs for cors, tts upstream, response parsing etc when debug mode is on
- update tts error response to use standardized json error format
- add dashboard and metrics path to cache-control exempt list

adapter/volcano/synthesis.go

@@ -8,6 +8,7 @@ import (
 	"log"
 	"time"
 
+	"github.com/volcano-tts/tts-api/common"
 	"github.com/volcano-tts/tts-api/dto"
 )
 
@@ -79,8 +80,10 @@ func Synthesis(
 		"X-Control-Require-Usage-Tokens-Return": "*",
 	}
 
-	log.Printf("TTS upstream: resource_id=%s speaker=%s model=%q format=%s sample_rate=%d speech_rate=%d additions=%q",
-		opts.ResourceID, opts.Speaker, opts.Model, opts.Format, opts.SampleRate, opts.SpeechRate, extractAdditionsForLog(body))
+	if common.DebugLog {
+		log.Printf("TTS upstream: resource_id=%s speaker=%s model=%q format=%s sample_rate=%d speech_rate=%d additions=%q",
+			opts.ResourceID, opts.Speaker, opts.Model, opts.Format, opts.SampleRate, opts.SpeechRate, extractAdditionsForLog(body))
+	}
 
 	resp, err := client.PostStream(ctx, "https://openspeech.bytedance.com/api/v3/tts/unidirectional", headers, body)
 	if err != nil {
@@ -129,6 +132,9 @@ func Synthesis(
 	}
 	mtr.UpstreamFinished(opts.Speaker, opts.Model, opts.Format, "ok", duration, parsed.FirstChunk, parsed.Chunks, len(finalData), 0)
 
+	log.Printf("TTS 合成成功 - 音色=%s 格式=%s 文本=%d字 音频=%d字节 分片=%d 耗时=%v",
+		opts.Speaker, clientFormat, len(text), len(finalData), parsed.Chunks, duration)
+
 	return &dto.SynthesisResult{
 		AudioData:  finalData,
 		Format:     finalFormat,