Add repo-specific AI workflow shortlist and high-confidence Copilot skills

[Copilot]

This PR reviews the repository for repeated manual workflows worth packaging and adds only the high-confidence missing assets. It documents what is worth standardizing, what should be skipped, and introduces narrow Copilot skills for the recurring chapter workflows most likely to benefit from consistency.

• Workflow shortlist

  • Adds AI_WORKFLOW_SHORTLIST.md with a compact, evidence-based inventory of repeated workflows.
  • Captures:
    • repeated workflow
    • supporting repo evidence
    • frequency/confidence
    • recommended packaging form
    • create/skip rationale

• New repo-specific Copilot skills

  • Adds focused skills under .github/skills for the recurring patterns found across chapter scripts, tests, and README guidance:
    • tiny-ps-chapter-test-loop
    • tiny-ps-deterministic-random
    • tiny-ps-input-normalization
    • tiny-ps-regex-text-transform

• Packaging decisions made explicit

  • Packages only workflows with strong repetition and stable inputs/outputs.
  • Deliberately leaves out lower-confidence or overlapping candidates such as release automation and cross-harness skill scaffolding.

• Resulting skill layout

.github/skills/
├── tiny-ps-chapter-test-loop/SKILL.md
├── tiny-ps-deterministic-random/SKILL.md
├── tiny-ps-input-normalization/SKILL.md
└── tiny-ps-regex-text-transform/SKILL.md