Build system: Migrate to pnpm+turborepo, re-organize workspace

[tokebe]

This PR re-organizes the build system such that:

• npm is replaced with pnpm for faster install/better workspace support
• Building uses turborepo for quicker/more intelligent build/task management
• The packages folder is now a flat directory
• Server code is moved to its own repo
• Many scripts and interactions are streamlined
• Typescript is better supported across the packages
• Deployment to npm is no longer a focus

[tokebe]

Note: currently failing tests due to SRI socket hang up, rather than any failing unit tests/other integration tests. PR passes all tests on local and is ready to move forward.