链接metamask移动app

**Describe the usability problem**
我开发了一个APP，用的flutter，需要通过我的APP打开metamask APP来获取地址和签名，我没有找到合适的样例或者开发文档

**Screenshots**
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**Expected behavior**
_If possible, a clear and concise description / resolution of what you expected to happen_

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_filled out after submission_

**User impact | Usage frequency | Feasibility scores**
_How important is this to the user, what the user wants to accomplish | Daily, weekly, monthly | Small, medium, large_

The issue names no files, tests, or entry points. Clarify the desired Flutter integration and acceptance criteria for obtaining an address and signature before locating the relevant mobile documentation or implementation.

Written by the indexing model from the issue text.