Add Antfly-native ingestion control plane

[jmcdermott45]

Summary

• add a protected Sources console for Antfly connector capabilities, sources, and durable jobs
• add server-only proxy routes for source creation, job submission, and cancellation
• define the versioned Antfly knowledge-ingestion integration contract
• keep connector execution, credentials, extraction, retries, and indexing in Antfly rather than Vercel

Backend boundary

The general connector API is intentionally documented as an Antfly backend dependency and is not presented as part of the current public OpenAPI surface. No local crawler or queue fallback is included.

Validation

• npm run lint
• npm run test:mcp
• npm run build
• git diff --check