feat: register pipeline C endpoints in the master openapi contract

[chetanr25]

Register Pipeline C endpoints in the master contract

Individual path files for Pipeline C (discussion #609) are in #618, #620, #622. This PR wires them into the root contracts/openapi.yaml.

Added

• GET /api/v1/extract/{extract_id}/readiness
• POST /api/v1/forms/generate (batch generation, one or many templates)
• GET /api/v1/forms/batch/{batch_id}/download
• GET /api/v1/templates/{template_id}/pdf
• GET /api/v1/templates/pdf/{upload_id}
• GET /api/v1/schema/fields

Removed

• POST /api/v1/forms/generate/all
• POST /api/v1/forms/generate/{form_type}