Initialize the shared NMFS OpenSci agent skills catalog

[Copilot]

Establishes an agent-independent catalog for portable NOAA Fisheries skills, with contribution conventions and automated validation. No skills or placeholder evaluations are introduced.

• Documentation: Defines catalog scope, maturity levels, installation guidance, skill structure, evaluations, and agent instructions.
• Collaboration: Adds focused issue forms and this pull request checklist.
• Validation: Adds dependency-free checks for frontmatter, naming, evaluation references, duplicate SKILL.md files, and common secret patterns.

Checklist

• The relevant issue is linked.
• The maturity level is appropriate.
• Each changed skill has a valid SKILL.md.
• Core instructions are concise and references are used appropriately.
• Bundled scripts are tested, or no scripts changed.
• Evaluations are added or updated when behavior changes.
• Current official documentation was checked where relevant.
• No secrets or sensitive information are included.
• The README catalog is updated if a skill was added, renamed, stabilized,
  deprecated, or removed.

• Fixes create the repo structure #1