Fix flake devshell wrt. Android SDK
social-app upstream seems to have bumped its SDK
Additionally, environment variable handling has been improved to avoid
impurities in the flake.
Verified by doing:
```sh
export NODE_ENV=production
yarn prebuild -p android && (cd ./android && ./gradlew assembleRelease)
```
authored by
tangled.org
f28351e6
d081c3aa