Allow evidence-bound fallback date approval

[seonghobae]

Summary

• keep embedded high-confidence production time as the only automatic date gate
• permit lower-ranked filename/filesystem evidence only with an exact immutable approved review decision
• require review for embedded dates below high confidence and mirror the backend policy in the UI
• keep the headless CLI fail-closed and preserve all copy, path, receipt, sync, and no-deletion invariants

Validation

• npm run check (0 errors, 0 warnings)
• npm test (5 files, 18 tests passed)
• git diff --check
• targeted Rust coverage added; remote CI is the authoritative compile/test because this disk-constrained host previously killed a clean Rust build under memory pressure

Formatting note

• repository-wide cargo fmt --check reports extensive pre-existing formatting drift outside this four-file change; no unrelated mechanical reformat was applied

Stack

• base: Add evidence-bound cloud review decisions #28