Switch from pnpm back to yarn classic

[taronaeo]

Everything works well when you do not have mono repo packages linking to one another. But once you start linking (e.g., @riva/shared package with @riva/portal), everything breaks down and fails to deploy.

The decision to switch to pnpm was primarily to be compatible with isolate-package which has since been tested to be running smoothly with yarn modern and classic as well.

Action: Discontinue usage of pnpm and swap back to yarn classic until Firebase starts supporting other package managers out of the box

[taronaeo]

As of right now, @riva/shared is declared as a dev dependency in @riva/portal (commit 2940db9) and that is not right.

The reason this works right now is because the shared code is mainly TypeScript models that get compiled into nothing. But once we factor in constant variables, everything will break.

[taronaeo]

An alternative solution is to use Cloudflare Worker sites which effectively works the same as Firebase Hosting for webframeworks. But it is currently un-tested and we won't know if it completely solves the problem or not.