fix(evidence): verify bounded integer local responses

[jeremi]

Summary

• map bounded-integer Evidence concepts to the existing integer form in local verification contexts
• cover the missing mapping with a focused regression test

User impact

evidencectl request prepare previously failed for otherwise valid projects containing a bounded-integer answer. This prevented the DHIS2 immunization tutorial, which has two bounded-integer concepts, from reaching request preparation.

Security-sensitive review note

This changes the closed expected-form mapping used to prepare offline local verification context. It does not expand source access, authentication, authorization, disclosure, signing, or network behavior. Integer response verification already exists; this patch makes bounded-integer concepts select that existing verifier form.

Verification

• cargo fmt --check
• cargo check --locked -p registry-evidence --all-targets
• cargo clippy --locked --profile ci --all-targets -p registry-evidence -p registry-mint -- -D warnings
• cargo test --locked -p registry-evidence (292 passed, 4 ignored)
• products/evidence/scripts/check-contracts.sh
• products/evidence/scripts/check-source-neutrality.sh
• clean DHIS2 tutorial replay through evidencectl request prepare with synthetic local inputs