Add Fabric integration to codebase

For beta launch on the 30th, integrate Fabric tracking so we can measure post-launch crashes and bugs.

https://docs.fabric.io/android/fabric/overview.html

Start with the linked Fabric Android overview and inspect the app's Android build and application entry points to determine where the integration belongs. Done means Fabric tracking is enabled for post-launch crashes and bugs as requested for the beta launch; no specific files or tests are named in the issue.

由索引模型根据 Issue 内容生成。