Fix CP1 atom identity and replay contracts

[NagisaVon]

Summary

• enrich extracted hunks with full Base/Final Git object OIDs and modes
• fingerprint binary/mode/symlink atoms from Git tree-entry identity and collapse mixed mode/text changes to one whole-file atom per path
• replace the misleading sequential-replay assertion with a real-Git Hypothesis property test in which every replay subset starts from the original Base
• add unit and integration regressions for binary identity, mode changes, and whole-file collapsing

The ignored local design/execution documents were updated alongside this PR with approved assumptions A15-A17. In particular, T05/T10 now treat remote generated refs as authoritative projection publication state and do not add projection OID fields to session JSON.

Validation

• ruff format --check .
• ruff check .
• mypy
• pytest -q (58 passed)