Feat: Improve Community Readiness and Open-Source Compliance

[ysorge]

Features:

• Add a CONTRIBUTING.md with coding standards, testing expectations, PR checklist, and review workflow.
• Add a CODE_OF_CONDUCT.md and GOVERNANCE.md (maintainer roles, decision-making, release responsibility).
• Add CITATION.cff and citation guidance for scientific reuse.
• Add issue/PR templates for bug reports, feature requests, and scientific-data-related edge cases.
• Add visible CI/quality badges in README (tests, coverage, package version, license).
• Expand contributor docs with a clear reproducible local workflow (editable install + test execution conventions).
• Clarify plugin contribution guidelines (API stability, expected interfaces, validation requirements).