Add a Ghost CMS connector

[eikiyo]

recto sources from and writes to WordPress (Application Password) and Webflow (API key). Add a Ghost connector behind the same interface so Ghost users can crawl pages and receive exact-paragraph link insertions via the Ghost Admin API.

Acceptance criteria

• New connector module mirroring the WordPress/Webflow shape (read published pages, write a link into published HTML).
• Credentials read from env and documented in .dev.vars.example.
• Unit test with a mocked Ghost Admin API.

Pointers: existing connectors live under recto/apps/workers/api/src.