Improve frontend startup without pdf service running

[manuelmeister]

I had the following errors:

✘ [ERROR] ENOENT: no such file or directory, open '/home/ecamp3/frontend/src/pdf/prepareInMainThread.mjs' [plugin vite:dep-scan]

    src/components/print/print-client/generatePdf.js:1:36:
      1 │ import { prepareInMainThread } from '@/pdf/prepareInMainThread.mjs'

✘ [ERROR] ENOENT: no such file or directory, open '/app/src/pdf/pdf.mjs' [plugin vite:dep-scan]

   src/components/print/print-client/renderPdf.js:3:32:
     3 │ import { render, prepare } from '@/pdf/pdf.mjs'

The missing files, pdf.mjs and prepareInMainThread.mjs, caused the problem due to a new repository installation where I forgot to run the client-side pdf service.

To help beginners, I have created a placeholder that gives a helpful suggestion instead of generating a vite error, and it is now possible to run the frontend without having to build the client-side pdf code.

To guide beginners to the correct package, all package.json names have been made consistent. Also the version field has been removed as it is not used and is unmaintained. Additionally they have been marked private.

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[BacLuc]

Could you please squash c6654dc
and 1df5114
That we don't have files in an ignored directory appear and disappear in the history.

What was the goal of changing the name and removing the version of our npm packages in the repo?
Could you mention the change and the reason in the PR description?

[manuelmeister]

@BacLuc done