feat: consolidate all skills into single-source references

[nicknisi]

Summary

• Move all 17 CLI skill files (AuthKit frameworks, backend SDKs, management) into references/ as the single source of truth
• Delete 6 AuthKit skill directories — replaced by CLI's canonical versions
• Only 2 registered skills remain: workos (router) and workos-widgets
• Add ESM package entry point (plugins/workos/index.ts) exporting path and content helpers for CLI consumption
• Update router with progressive disclosure for all references: AuthKit frameworks, backend SDKs, language detection, management
• Simplify eval runner — all skills now load from references/
• Rewrite README with npm usage docs

Context

The workos CLI and this marketplace plugin both maintained AuthKit skill files independently. They diverged over time (different README URLs, different gotchas, CLI had SvelteKit while this repo didn't). This PR makes @workos/skills the single source of truth. The CLI will consume this package and inject reference content directly into the agent prompt.

npm Package Usage

After publishing, the CLI (or any consumer) can import content helpers:

npm install @workos/skills

import { getReference, getSkill } from '@workos/skills';

// Read reference content directly
const content = await getReference('workos-authkit-nextjs');

// Read a skill's SKILL.md content
const router = await getSkill('workos');

Path helpers are also available for consumers that need file paths (e.g., skill discovery):

import { getReferencePath, getSkillsDir, getSkillPath } from '@workos/skills';

const refPath = getReferencePath('workos-authkit-nextjs'); // absolute path to .md file
const skillsDir = getSkillsDir();                          // directory containing workos/ and workos-widgets/
const skillPath = getSkillPath('workos');                   // absolute path to SKILL.md

Exports

Function	Returns
getReference(name)	Promise<string> — reference file content
getSkill(skillName)	Promise<string> — skill SKILL.md content
getReferencePath(name)	Absolute path to references/{name}.md
getSkillsDir()	Absolute path to the skills/ directory
getSkillPath(skillName)	Absolute path to skills/{skillName}/SKILL.md

Architecture

Marketplace plugin:  Router (SKILL.md) → Read references/*.md → agent fetches docs
CLI (post follow-up PR): buildIntegrationPrompt() → await getReference(name) → inject into prompt

• 40 reference files (22 original topic files + 17 from CLI + 1 integrations router)
• 2 registered skill directories: workos/ and workos-widgets/
• ESM entry point: plugins/workos/index.ts

Test plan

• pnpm test — 182 tests pass
• pnpm lint — 0 warnings, 0 errors
• pnpm eval -- --dry-run — 42 cases load
• pnpm eval -- --no-cache --case=authkit-nextjs-setup — +19% delta
• CLI evals with linked package — 62/62 passed (100%), no regression vs pre-consolidation
• workos skills list shows 2 skills from package
• workos skills install/uninstall works with package-sourced skills
• Manual Next.js 16 install flow — successful