[PierreRaybaut]

Summary

Support raw single-file Desktop plugins in the public catalog, alongside existing wheel distributions.

Refs DataLab-Platform/DataLab#419. Desktop implementation: DataLab-Platform/DataLab#420, targeting develop.

Changes

• First clarify that source organization and distribution are independent: a layered project is not an API requirement.
• Extend the YAML schema with optional kind: module, an exact GitHub release asset filename and explicit public metadata, including version, description and an accepted source license.
• Inspect Python syntax, encoding, names, sizes and safely readable metadata without importing or executing scripts. Keep the inspector synchronized with Desktop via a verbatim-copy equality test.
• Mirror exact source bytes under modules/<sha256>/... using relative URLs, so the published JSON and files also work as an offline catalog.
• Label module entries as Python file and restrict them to Desktop. Existing wheel defaults, Web targets and wheel dependencies remain unchanged.
• Document unchanged historical files, metadata overrides, stable file names, version/revision tracking and offline transfer.

Validation

• 38 publication tests passed, including an end-to-end test that installs the generated offline mirror with the updated Desktop client.
• Cover exact asset selection, non-execution, invalid/empty source, metadata identity/version conflicts and unsupported PyPI module sources.
• Inspector equality and Ruff checks passed.
• The optional Desktop integration test requires the updated client; standalone publication tests continue to run with the latest released DataLab reference environment.
• Inspect module specs before the optional integration test: released DataLab 1.3 still has a Qt-dependent plugins.py, so probing a child module by importing that legacy host would unnecessarily require Qt in the catalog CI. A regression test covers that case without masking errors in an actually available updated client.

Deployment

No Camera/Pulse entries are changed and no new plugin release or example is published by this PR. Actual module entries require the updated Desktop client; old wheel-only clients skip .py releases as non-installable. DataLab-Web itself is out of scope.