chore: split scan completeness reporting into focused pull requests

[luojiyin1987]

PR #893 combines scanner completeness, output presentation, multi-folder aggregation, and ratchet behavior.

Track the remaining work after the scanner core PR:

• Add JSON, terminal, and HTML completeness diagnostics.
• Aggregate diagnostics for multi-folder output.
• Block ratchet baseline work when detection data is incomplete.

The scanner core PR only adds the model, diagnostics collection, registry observer support, and result propagation.

Progress update:

• Scanner completeness model and diagnostic collection — feat(scanner): track scan completeness #908
• Terminal, JSON, HTML, and multi-folder reporting — feat(output): report scan completeness #936
• Ratchet/baseline rejection for incomplete detection data — fix(ratchet): reject incomplete detection data #937

Both remaining PRs are ready for review and all checks are passing.

[sonukapoor]

Thanks for splitting this out @luojiyin1987, that is exactly the right call. The staged breakdown (data model and scanner tracking first, then reporting, then ratchet handling) makes each piece reviewable on its own. I am looking at #908 now as part 1, and I will keep this tracking issue open until the series lands.