Modularize knowledge and consolidation module surfaces

[yvette-carlisle]

Summary

• split knowledge readback DTOs and source snapshots into focused Rust modules
• split consolidation proposal storage and promotion payload helpers by operation
• split knowledge source storage and memory correction storage into explicit module boundaries

Validation

• RUSTC=/run/current-system/sw/bin/rustc cargo make fmt-rust && RUSTC=/run/current-system/sw/bin/rustc cargo make check after each segment
• final segment validation: 403 nextest tests passed, 92 skipped

Batch size

• 35 files changed, 1929 insertions, 1785 deletions versus origin/main