fix(部署): 配置文件挂载改为可选，避免 Docker 自动创建目录

当挂载的源文件不存在时，Docker 会自动创建同名目录而非文件。
将配置文件挂载默认注释，用户需要时先创建文件再取消注释。

🤖 Generated with [Claude Code](https://claude.com/claude-code

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

deploy/docker-compose.yml

@@ -28,8 +28,9 @@ services:
     volumes:
       # Data persistence (config.yaml will be auto-generated here)
       - sub2api_data:/app/data
-      # Mount custom config.yaml (optional, overrides auto-generated config)
-      - ./config.yaml:/app/data/config.yaml:ro
+      # Optional: Mount custom config.yaml (uncomment and create the file first)
+      # Copy config.example.yaml to config.yaml, modify it, then uncomment:
+      # - ./config.yaml:/app/data/config.yaml:ro
     environment:
       # =======================================================================
       # Auto Setup (REQUIRED for Docker deployment)