test(arrr): prepare unsigned local QDN fixture

[QuickMythril]

Summary

• add an opt-in preparer for a retained, disposable local-QDN Pirate Unified fixture
• seed the fixture through Core's production writer and repository with a deterministic placeholder signature, without signing, importing, broadcasting, confirming, or minting
• reopen the on-disk repository and rebuild the exact staged bundle through the pinned transaction-data reader with missing-file network requests disabled
• document the synthetic-fixture boundary and keep ordinary production QDN loading behavior unchanged

Validation

• real staged bundle fixture: 1 test, 0 failures, 0 errors, 0 skipped
• focused Pirate/QDN suite: 23 tests, 0 failures, 0 errors, 3 expected opt-in skips
• full Core suite: 3,266 tests, 0 failures, 0 errors, 70 expected skips across 366 isolated Surefire reports
• shell syntax, ShellCheck, and git diff --check pass
• independent review: SHIP after the local reader was made fail-closed against missing-file network requests

Boundaries

• the retained repository row is synthetic and is not a QDN publication or peer-retrieval result
• no packaged Core or native code is executed in this PR
• no wallet is initialized, synchronized, funded, signed, or used for a transaction
• no QDN publication, deployment, default enablement, or Home change