Feature/Fix: Classify shadow lineage residuals

[iam-brain]

Summary

• add a conservative classifier for differences between legacy, lineage, and finalized UTC usage totals
• keep provisional reference days out of acceptance math and require explicit evidence before assigning unavailable history
• validate the July 9–11 sanitized replay, where aggregate absolute error drops from 810.3M to 103.4M tokens, while preserving ordinary-day parity checks
• reject invalid evidence and keep aggregate/tolerance arithmetic overflow-safe

This is the residual-classification slice of the planned scanner rearchitecture. It does not change production accounting totals.

Closes #16.

Validation

• swift test --filter CodexLineageResidualClassifierTests
• make check
• env SDKROOT=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX26.5.sdk make test (642 selections passed)