Gate loopback logs behind DEBUG env

src/config.ts

@@ -15,6 +15,10 @@ const envSchema = z.object({
   LOCAL_AI_VENV_PATH: z.string().min(1).default(".local-ai/.venv"),
   LOCAL_AI_PYTHON: emptyToUndefined,
   AUDIO_SOURCE: emptyToUndefined,
+  DEBUG: z
+    .string()
+    .optional()
+    .transform((value) => value?.trim().toLowerCase() === "true"),
   WHISPER_MODEL: z.string().min(1).default("large-v3-turbo"),
   WHISPER_LANGUAGE: z.string().min(1).default("ko"),
   WHISPER_DEVICE: z.enum(["auto", "cuda", "cpu"]).default("auto"),