refactor(schemas): migrate maturity metadata to registry, remove from frontmatter

[Copilot]

• Explore and understand all files requiring changes
• Phase 1: Schema Updates — Remove maturity property from 5 schema files
• Phase 2: Artifact Frontmatter Removal — Remove maturity line from all artifact files
• Phase 3: Documentation Updates — Update docs to reference registry
  • Step 3.1: Rewrite ai-artifacts-common.md maturity section
  • Step 3.2: Remove maturity from custom-agents.md
  • Step 3.3: Remove maturity from instructions.md
  • Step 3.4: Remove maturity from prompts.md
  • Step 3.5: Remove maturity from skills.md
  • Step 3.6: Update release-process.md maturity section
  • Step 3.7: Update prompt-builder.instructions.md — add registry maturity guidance
  • Step 3.8: Update pull-request.prompt.md maturity detection
• Run code review and security checks — ✅ No issues

Security Summary: No security vulnerabilities. All changes are documentation and JSON schema modifications only.

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[katriendg]

@copilot the instructions in this file need to be updated: ./.github/instructions/prompt-builder.instructions.md to include the new guidance see all references to maturity and update accordingly.
Also the following note is no longer relevant

Note: VS Code shows a validation warning for the maturity: field as it's not in VS Code's schema. This is expected; the field is required by the HVE-Core codebase for artifact lifecycle tracking. Ignore VS Code validation warnings for the maturity: attribute.

also search other files in .github/ that may still reference the wrong guidance for maturity, if any are left

[Copilot]

@copilot the instructions in this file need to be updated: ./.github/instructions/prompt-builder.instructions.md to include the new guidance see all references to maturity and update accordingly.
Al...

Updated in 628dc1d. Added registry maturity guidance to the Frontmatter Requirements section of prompt-builder.instructions.md: "Maturity is tracked in .github/ai-artifacts-registry.json, not in frontmatter. Do not include a maturity field in artifact frontmatter." The VS Code warning note was already removed in a prior commit. Searched all other .github/ markdown files — remaining maturity references are all in pull-request.prompt.md (already updated to reference registry) and ai-artifacts-registry.json (the registry itself). No stale guidance found.

[katriendg]

@copilot attach this to #438 and update the issue to reflect what is done

[Copilot]

@copilot attach this to #438 and update the issue to reflect what is done

I'm unable to link PRs to issues or update issue descriptions — those operations require GitHub API access that isn't available in my environment. You can link this PR to #438 by adding Closes #438 or Fixes #438 to the PR description, or by manually linking it in the issue sidebar.