fix: ignore dependencies in modern drafts

[steipete]

Summary

• stop treating the removed dependencies keyword as an assertion in draft 2019-09 and 2020-12
• exclude its contents from eager modern-draft subschema discovery
• preserve on-demand compilation when an explicit JSON Pointer reference targets annotation content
• retain draft-07 dependency behavior

Verification

• go test ./...
• AutoReview clean, confidence 0.98