Add a JobPosting named schema to the extract tool

[KnockOutEZ]

The extract tool ships named schemas (Article, Recipe, Product, CodeSnippet, Paper, EventListing) that pull structured data from pages, preferring JSON-LD when a page provides it. JobPosting is a standard schema.org type that job boards emit as JSON-LD — a natural next schema, and the existing ones are small self-contained files.

Where to look

• Template to copy: src/extraction/v1/schemas/EventListing.ts (JSON-LD first, DOM fallback)
• Schema routing: src/extraction/v1/classifier.ts (accepts "JobPosting", "schema:JobPosting", schema.org URL forms)

Acceptance

• src/extraction/v1/schemas/JobPosting.ts with fields like title, company, location, salary (when present), employment type, posted date — null when absent, never invented
• Wired into the classifier + the extract tool's named_schema enum
• Unit test with a JSON-LD fixture
• npm test and npm run lint green