[Feature] Define `/workflows` as portable agentic workflow source

[ashleyshaw]

Summary

Create the first portable workflow source model under /workflows, distinct from executable GitHub Actions in .github/workflows.

Parent epic: #283.

Proposed Solution

Add /workflows/README.md plus one or two placeholder workflow specs showing how portable AI workflows should be documented and later packaged into plugins or skills.

Acceptance Criteria

• /workflows is documented as agentic workflow source, not GitHub Actions.
• .github/workflows remains the executable GitHub Actions folder.
• At least one example portable workflow spec exists.
• Links to related skills or agents are included.
• Documentation/changelog updated.
• Tests added/updated if validation covers workflow specs.
• PR uses correct branch prefix feat/.

[linear-code]

LS-613

[ashleyshaw]

Completed and verified locally.

Evidence:

• Portable workflows source report: .github/projects/active/portable-ai-plugin-restructure/portable-ai-plugin-restructure-portable-workflows-source-report-2026-05-26.md
• Workflow ownership index: workflows/README.md
• Example portable workflow spec: workflows/portable-ai-plugin-restructure.md

Completed outcomes:

• /workflows is documented as the portable agentic workflow source.
• .github/workflows/ remains the executable GitHub Actions folder.
• Added the first example workflow spec with inputs, outputs, steps, guardrails, and related assets.
• Linked related agent, instruction, and skills assets.

Verification run on 2026-05-26:

• npx markdownlint-cli2 "workflows/*.md" ".github/projects/active/portable-ai-plugin-restructure/portable-ai-plugin-restructure-portable-workflows-source-report-2026-05-26.md" passed with 0 errors.
• npm run validate:structure passed.
• git diff --check passed.