Add actionable gap ledger

[dorkalev]

Summary

Add a first-class gap ledger that turns criterion maturity into explicit next actions.

Tickets

Fixes #20

Changes

• partition every in-scope criterion into build/fix, prove-operation, or review-over-time
• show counts, plain-language explanations, next actions, and criterion evidence links
• keep the Type II observation-period gap separate and explicitly not evaluated
• renumber the working-paper sections and document the classification contract
• add regression coverage proving that every in-scope criterion appears exactly once

Test Plan

• cargo test --manifest-path website/app/Cargo.toml --locked
• render the current production database and confirm 8 build/fix, 14 prove-operation, and 14 review-over-time criteria
• confirm out-of-scope criteria do not appear in the gap ledger