Fix Zenodo GitHub link by correcting CITATION.cff metadata

[Copilot]

The Zenodo GitHub integration was failing due to invalid metadata in the CITATION.cff file. This prevented proper citation generation and DOI assignment through Zenodo's automatic GitHub integration.

Issues Fixed

The CITATION.cff file contained several validation errors:

1. Invalid DOI placeholder: The file contained doi: .. which is not a valid DOI format
2. Incorrect date format: Used 15.08.2025 instead of the required ISO 8601 format 2025-08-15
3. Invalid license identifier: Used "LGPL-3.0 license" instead of the SPDX identifier LGPL-3.0-only

Changes Made

• Removed the invalid DOI placeholder (the DOI field is optional and can be added later when a DOI is assigned)
• Corrected the release date format to comply with ISO 8601 standard
• Updated the license field to use the proper SPDX license identifier

Validation

The corrected file now:

• ✅ Passes official Citation File Format validation
• ✅ Successfully converts to BibTeX format
• ✅ Successfully converts to Zenodo metadata format
• ✅ Enables proper GitHub-Zenodo integration

# Before (invalid)
date-released: 15.08.2025
doi: ..
license: "LGPL-3.0 license"

# After (valid)
date-released: 2025-08-15
# doi field removed (can be added when DOI is available)
license: LGPL-3.0-only

Fixes #2167.

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