Fix up workspace structure

[pileks]

This fixes the bad strip-ansi resolution for react-scripts:

  "resolutions": {
    "react-scripts/**/strip-ansi": "6.0.1"
  },

In order to properly add dependencies/dev dependencies, the paths to our packages should not start with a trailing ./:

  "workspaces": {
    "packages": [
      "packages/*",
      "apps/*"
    ],
    "nohoist": ["gpt-tokenizer"]
  },

For reference: yarnpkg/yarn#4878 (comment)