REUSE compliance

[brownbaerchen]

We have promised in the HeatHub project to achieve and enforce REUSE compliance. This is about licensing. We need to specify a license and integrate the reuse linting tool to check the licensing.

Now, we already have a LICENSE file, which specifies MIT license globally and we don't want to change that at this time. However, this is apparently not machine readable. In order to make the machine accept our global license, we need to move the license to LICENSES/MIT.txt and specify that this should apply globally in REUSE.toml. Annoyingly, we cannot merge that with pyproject.toml at this time.

Note that the linter runs on push to main, which is sufficient because added files will automatically fall under the global license. So the only way to fail the linter is to change the licenses in REUSE.toml.
In order to create the proper badge, we need to merge this first so the action on push to main is actually triggered. Then we can address #2318 and replace the fake badge from here with a proper one.

Changes proposed:

• Implement reuse linting GitHub workflow on push to main
• Make global MIT license machine readable
• Reference original licenses of datasets packaged with Heat
• Remove unused images

Type of change

Delivering deliverables

Does this change modify the behaviour of other functions? If so, which?

no

[Copilot]

Pull request overview

This PR introduces REUSE compliance infrastructure for the Heat repository by adding a REUSE configuration, moving the MIT license text into the REUSE-expected LICENSES/ layout, and wiring up CI to lint licensing metadata.

Changes:

• Add REUSE.toml with global MIT licensing annotations and per-dataset overrides.
• Add LICENSES/MIT.txt and update the README to reference the new license location and include a REUSE status badge.
• Add a GitHub Actions workflow to run reuse lint in CI.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 5 comments.

File	Description
REUSE.toml	Defines global SPDX annotations and dataset-specific license overrides for REUSE linting.
README.md	Adds a REUSE badge and updates the license link to the new LICENSES/MIT.txt path.
LICENSES/MIT.txt	Provides the MIT license text in the machine-readable location expected by REUSE.
.github/workflows/reuse_compliance.yml	Adds CI automation to run reuse lint.

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[brownbaerchen]

We need to use a status badge for push to main because this is part of that action, actually.