Feature/Fix: Bound lineage reconciliation work

[iam-brain]

Summary

• prepare deterministic, home-scoped lineage families with SHA-256 fingerprints
• reuse unchanged family results through an immutable in-memory candidate cache
• recompute only families affected by changed evidence or newly discovered parents
• make cancellation and publication atomic while reporting honest structural peak metrics

This isolated scanner-rearchitecture component bounds reconciliation scratch state to the largest family. End-to-end scan memory still requires the follow-up two-pass discovery work tracked in #33.

Closes #17

Validation

• swift test --filter CodexLineageEngineTests (8 passed)
• make check
• env SDKROOT=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX26.5.sdk make test (643 selections, 54 groups, no failures or retries)