feat(skills): make skills directory configurable via module options

[francoisauclair911]

Summary

• Adds a dir option to the skills Nuxt module so users can specify a
  custom skills directory instead of the hardcoded skills/ default
• Fully backward compatible — defaults to 'skills' when not set
• Documents the new option in both English and French docs

Usage

// nuxt.config.ts
export default defineNuxtConfig({
  skills: {
    dir: 'agent-skills'
  }
})

Changes

• layer/modules/skills/index.ts — added ModuleOptions interface, typed
  defineNuxtModule<ModuleOptions>, added defaults: { dir: 'skills' },
  replaced hardcoded path with options.dir
• docs/content/en/4.ai/3.skills.md — added Configuration section
• docs/content/fr/4.ai/3.skills.md — added Configuration section (French)

Test plan

• Run pnpm playground:dev and confirm skills/ is still discovered by default
• Add skills: { dir: 'custom-dir' } to playground/nuxt.config.ts, create
  a skill there, and confirm it is served at /.well-known/skills/
• Confirm /.well-known/skills/index.json returns the correct skill

[vercel]

Someone is attempting to deploy a commit to the NuxtLabs Team on Vercel.

A member of the Team first needs to authorize it.

[larbish]

Thanks for your PR! I'll merge this one but I will provide an update in a following PR to expose both assistant and skills config keys in a docus parent.

So once both PR merged and released, you'll have to move your skills dir config in a docus parent.

I'll update doc ofc.

[larbish]

👉 #1346