Update setup for type-css-modules

[ijlee2]

While working on #177, I realized that a race condition can happen between lint:format and prelint:types, when an end-user's project uses prettier directly to format their code.

Error message from https://github.com/ijlee2/embroider-css-modules/actions/runs/16670201547/job/47184555490:

[lint:format] [error] Unable to read file "app/assets/app.css.d.ts":
[lint:format] [error] ENOENT: no such file or directory, open '/home/runner/work/embroider-css-modules/embroider-css-modules/docs/my-v1-app/app/assets/app.css.d.ts'

Find a more resilient way that ensures that CSS declaration files exist before lint:format runs.