fix: 修复 MiMo ASR endpoint 路径重复拼接导致 404 的问题

config.yaml 中 endpoint 已包含 /chat/completions，而 mimo.go 会自动拼接该路径，
导致实际请求地址变为 .../chat/completions/chat/completions。

- config.yaml: endpoint 改为 base URL https://api.xiaomimimo.com/v1
- .env.example: STT endpoint 示例更新为 MiMo 地址

.env.example

@@ -11,7 +11,7 @@ CAMTALK_AI_TTS_API_KEY=
 # CAMTALK_AI_LLM_MODEL=gpt-4o
 # CAMTALK_AI_LLM_ENDPOINT=https://api.openai.com/v1
 # CAMTALK_AI_LLM_TIMEOUT=10
-# CAMTALK_AI_STT_ENDPOINT=wss://api.deepgram.com/v1/listen
+# CAMTALK_AI_STT_ENDPOINT=https://api.xiaomimimo.com/v1
 # CAMTALK_AI_TTS_ENDPOINT=https://api.openai.com/v1
 # CAMTALK_AI_TTS_VOICE=alloy
 # CAMTALK_AI_TTS_SPEED=1.0