[fix] Add start-files.json

[timroes]

Add a script that'll generate a list of all "starter files", i.e. all files that are included in the starter repository and stops attaching data-zite-id to elements, if the file path would be a starter file, since those are the cases that'll later crash the editor (see https://linear.app/fillout/issue/ZIT-2867/editor-crashes-when-editing-child-element-of-component).

The way we're uploading edited files later, I didn't see a cleaner way to do that, than have that list comitted. However if reviewers know a way of determining without that list later on, if a file is part of the starter files or part of the LLM generated ones, happy to change to a new approach.

Also add a github workflow that makes sure that list is updated in a PR, and otherwise fail the PR (see https://github.com/zite/zitejs-starter/actions/runs/22096567870/job/63855082206 for an example of the failure).

[timroes]

Talked to @Awendel and he'll add a fix for this as part of his PR on working on Selective Editing.