feat: 新增语音转文字（ASR）功能

- 后端：新增 /api/audio/transcribe 接口，调用 Ollama whisper 进行语音识别
- 前端：新增 AudioTranscribePage.vue 页面，支持 MP3/WAV/M4A/OGG/FLAC 等格式
- 注册路由、工具卡片、智能助手欢迎语更新

Co-Authored-By: Claude Code <noreply@anthropic.com>

eai_agentplatform/backend-go/config/ai_secrets.example.json

@@ -0,0 +1,12 @@
+{
+  "VECTORENGINE_API_KEY": "sk-...",
+  "OPENROUTER_API_KEY": "sk-or-...",
+  "VOLCES_API_KEY": "",
+  "LMUAI_API_KEY": "sk-...",
+  "ALIYUN_API_KEY": "sk-...",
+  "DEEPSEEK_API_KEY": "sk-...",
+  "REMOVE_BG_API_KEY": "",
+  "ANTHROPIC_API_KEY": "",
+  "OPENAI_API_KEY": "",
+  "BRAVE_SEARCH_API_KEY": "BSA..."
+}