QQ Bot Go API Server

Auth: All [auth] endpoints require "Authorization: Bearer <api_token>" header
      (server.token in config.yaml, always required)

Endpoints:
  POST /send          - Send a message [auth required]
    Body: {"to": "openid", "text": "hello", "type": "c2c|group", "image_url": "..."}

  GET  /users         - List known users [auth required]
    Query: type=c2c|group|channel, limit=N

  GET  /users/stats   - User statistics [auth required]

  POST /broadcast     - Broadcast message to all known users [auth required]
    Body: {"text": "hello", "type": "c2c|group", "limit": N}

  GET  /health        - Health check