feat(skills): add agentforge-workflow skill + Vercel publish flow

[mandarnilange]

Summary

• Adds skills/agentforge-workflow/ — a guided AgentForge workflow author for any AI coding agent (Claude Code, Cursor, Codex). Walks the user through goal → template check → agent decomposition → pipeline shape → flows → nodes → schemas, then emits a complete .agentforge/ directory. On-demand reference cheat sheets cover agent / pipeline / node schemas, the template catalog, and scaffold layout.
• Adds a Vercel-skills publish flow: scripts/validate-skills.mjs + .github/workflows/publish-skills.yml validate frontmatter (name, description, license, metadata.author, metadata.version) and enforce the agentforge- name prefix on every PR. The skills/ directory IS the publication — no upload step. Once merged, the skill is installable via npx skills add mandarnilange/agentforge/agentforge-workflow.
• Restructures the README (~52% shorter): hero stays clean, harness model lands right after Quick Start (was buried at line 249), audience pitch / package comparison / harness deep dive moved to dedicated docs, and all doc links consolidated into one grouped "Learn more" launchpad (Get started · Concepts · Operate · Extend & test).
• New docs preserve the dropped content: docs/who-uses-it.md, docs/harness-model.md, docs/packages.md, docs/artifacts.md. docs/platform-architecture.md gains a heterogeneous worker pool deployment example (§15).

How to install the skill (after merge)

# Just this skill
npx skills add mandarnilange/agentforge/agentforge-workflow

# All skills in the repo
npx skills add mandarnilange/agentforge

Trigger it in any session with prompts like "help me design an AgentForge pipeline for PR triage" or "what agents do I need to build an SEO audit workflow?".

Test plan

• npm run skills:validate passes locally and in CI
• Publish Skills workflow turns green on this PR
• All 11 doc links in the README's "Learn more" section resolve
• gh pr checks reports green on existing CI (lint / build / test)
• Manually trigger the skill in a Claude Code session against a fresh repo and confirm it produces a valid .agentforge/ directory that agentforge validate accepts