chore: remediate repo standards gaps

[mcj-coder]

Summary:

• Add Nx monorepo configuration for per-skill independent versioning and tags
• Enforce default-branch commit guardrail and document branch protection
• Add Secretlint CI and Nx Release tagging workflow
• Document CI/CD scope and per-skill tag policy

Details:

• Nx projects defined per skill with tag pattern skill/<name>/vX.Y.Z
• Default-branch guardrail added to .husky/pre-commit
• CI adds Secretlint and Nx Release (tags only)

Verification:

• npm run verify
• npx nx graph --file=.tmp/nx-graph.json --watch=false
• npx nx release --dry-run --projects=architecture-testing --verbose

Notes:

• Full nx release dry-run for all skills timed out; single-project dry-run verified tag format