E3.2: Remove review packet policy drift across modes

[agustif]

Parent epic: #209
Program: #206

Centralize packet policy fields and remove mode-specific divergence.

Acceptance

• Packet semantics are identical across review modes for shared options.
• Existing drift (max_files_per_batch, config redaction, next-command shaping) resolved.

[agustif]

Implemented in PR #228 (commit cd91f96).

State update:

• Shared packet fields now flow through one coordinator path for prepare, run-batches, and external-start.
• max_files_per_batch, config redaction, retrospective option shaping, and narrative injection now converge through one builder contract.
• Added parity regression test (test_review_packet_shared_fields_match_across_modes) to prevent policy drift reintroduction.

Validation: targeted + broad review tests passed (103 passed).

[agustif]

Completed via implementation PR(s) in this program. Closing as done.