fix priming validation and plan contract

[dapi]

Summary

• reject priming manifest paths whose remainder becomes absolute outside the payload scope
• add regression coverage and run it in CI
• align the feature implementation-plan template with the Plan Ready priming metadata contract

Validation

• ruby tools/validate-priming-manifests-test.rb
• ruby tools/validate-priming-manifests.rb template/memory-bank
• memory-bank-cli lint --scope-root template/memory-bank --entrypoint template/memory-bank/README.md
• memory-bank-cli doctor --profile template
• git diff --check