Split consolidation proposal review storage

[yvette-carlisle]

Summary

• move consolidation proposal review-event insert/list persistence into a private sibling module
• keep the public elf_storage::consolidation re-exports unchanged
• reduce proposals.rs to proposal row persistence only

Validation

• cargo make fmt-rust
• cargo make check-rust
• cargo make lint-vstyle
• cargo make lint-rust
• cargo make test-rust: 370 passed / 92 skipped
• cargo make check: 370 passed / 92 skipped
• cargo make test-rust-integration: 92 passed / 370 skipped
• cargo make check-trace-gate
• git diff --cached --check

Skeptic review found no blockers and recommended commit.