[Core] Support YAML-based archetype files #17

Allow archetypes to be defined in .yml files instead of only in TypeScript.

Why: This makes it much easier for non-developers to contribute archetypes. They can submit a YAML file without knowing TypeScript.

Format:

id: mobile-engineer
name: Mobile Engineer
description: iOS/Android engineers
keywords:
  - swift
  - kotlin
  - react native
evaluationWeights:
  shippedEvidence: 0.25
  quantifiedImpact: 0.20
  # ...
actionVerbs:
  - Built
  - Shipped
antiPatterns:
  - 'familiar with mobile development'

Implementation:

• Add a loader that reads from archetypes/*.yml
• Validate against the RoleArchetype interface
• Register them alongside the built-in ones