Move reference results metadata into each archive

[PranjalManhgaye]

Summary

• Store reference-results-metadata.txt inside each archive's case directory

• Stop writing one shared metadata file per tutorial

• Drop the SHA256 checksum from the metadata (it described the outer .tar.gz, which no longer makes sense once the file lives inside that archive)

• Ignore the embedded metadata during field comparison

• Rename the metadata file to reference-results-metadata.txt so editors open it as plain text

• Update the system-test documentation

Closes #811

Test Plan

Packed sample archives locally and verified reference-results-metadata.txt ends up inside each case folder, with exports and iteration logs unchanged, and no shared metadata file written anymore. Also verified fieldcompare ignores the metadata file, and ran pre-commit on the changed files. Full regeneration of reference archives happens after merge, as discussed.

[MakisH]

Looks good. I would further simplify and polish the template, but I can directly do that in a separate PR.

[MakisH]

The system tests are now failing, complaining about the fieldcompare option:

#8 resolving provenance for metadata file
#8 DONE 0.0s
[stderr]  Image breaking-dam-2d_fluid-openfoam-solid-calculix_2026-08-10-035105-field-compare Built 
[stderr] time="2026-08-10T03:51:43+02:00" level=warning msg="Found orphan containers (breaking-dam-2d_fluid-openfoam-solid-calculix_2026-08-10-035105-solid-calculix-1, breaking-dam-2d_fluid-openfoam-solid-calculix_2026-08-10-035105-fluid-openfoam-1, breaking-dam-2d_fluid-openfoam-solid-calculix_2026-08-10-035105-prepare-1) for this project. If you removed or renamed this service in your compose file, you can run this command with the --remove-orphans flag to clean it up."
[stderr]  Container breaking-dam-2d_fluid-openfoam-solid-calculix_2026-08-10-035105-field-compare-1 Creating 
[stderr]  Container breaking-dam-2d_fluid-openfoam-solid-calculix_2026-08-10-035105-field-compare-1 Created 
Attaching to field-compare-1
[stderr]  Container breaking-dam-2d_fluid-openfoam-solid-calculix_2026-08-10-035105-field-compare-1 Starting 
[stderr]  Container breaking-dam-2d_fluid-openfoam-solid-calculix_2026-08-10-035105-field-compare-1 Started 
[stderr] field-compare-1  | usage: fieldcompare [-h] [--version] {file,dir} ...
[stderr] field-compare-1  | fieldcompare: error: unrecognized arguments: --exclude-files reference-results-metadata.txt --ignore-unsupported-file-formats

I did not expect this to fail, but it looks like the fieldcompare version we use is too old: https://github.com/dglaeser/fieldcompare-action

I will contribute upstream. -> dglaeser/fieldcompare-action#15

edit: Since this is anyway trivial, I dropped the dependency in #895