Issue 508 — Add portable DepMap report snapshot exporter

[rsolerortuno]

Summary

Implements Issue 508: Portable DepMap report snapshot.

• Adds an offline, fail-closed exporter for validated DepMap v0.5.0 releases.
• Produces deterministic, repository-safe reporting snapshots.
• Validates release identities, reproducibility, baseline preservation, disabled activation, and mandatory human review.
• Streams selected target profiles without copying the complete JSONL artifact.
• Adds deterministic checksums, path sanitization, and safe overwrite handling.
• Uses lightweight synthetic fixtures only.

Scientific boundaries

• The original 300-gene production baseline remains unchanged.
• Baseline scores and ranks remain unchanged.
• No candidate activation is enabled.
• Human review remains mandatory.
• DepMap cell-line dependency is not treated as clinical anti-PD-1 response evidence.
• No complete matrices or real release artifacts are committed.

Validation

• Issue 508 tests: 33 passed.
• Directed release and documentation tests: 25 passed.
• Full repository suite: 722 passed.
• AGY adversarial audit: completed.
• Claude review: approved.
• git diff --check: passed.

The real DepMap Public 26Q1 snapshot remains deferred to Issue 512.