Add workflow to protect from uncomitted LLM text files changes

[FranjoMindek]

Detects if there are any missing changes to LLM text files if we made changes to opensaas-sh docs.

Here is how it looks like when it:

1. fails: https://github.com/wasp-lang/open-saas/actions/runs/17981743175/job/51149343704?pr=514
2. passes: https://github.com/wasp-lang/open-saas/actions/runs/17981869647/job/51149798437?pr=514

Vibecoded but edited manually to fix echo + quiet mode diff.

[infomiho]

Hey we did this a bit differently in the https://github.com/wasp-lang/wasp repo, we don't keep the llms.txt in version control but generate them when we build the docs.

• Running on Cloudflare on deploy
• The build script https://github.com/wasp-lang/wasp/blob/main/web/package.json#L10
• Ignoring llms.txt in .gitignore https://github.com/wasp-lang/wasp/blob/main/web/.gitignore#L23

[FranjoMindek]

Oh didn't know we did that already on wasp.
I will modify the current approach to be same as above then. Much better than duplicating same changes in diffs.
Thanks.