Fix ZK verifier mode handling

[quangvdao]

Summary

• Derive the modular verifier ZK mode from proof.claims.is_zk() in helper/example/generated verifier paths.
• Preserve standard proof behavior while allowing ZK proofs to reach the committed sumcheck and BlindFold verifier path.

Root Cause

Some verifier call sites passed zk = false unconditionally after the modular verifier split. That causes valid ZK proofs to fail consistency checks as if they were clear proofs.

Validation

• cargo fmt -q
• cargo check -q -p jolt-sdk --tests --features host
• cargo check -q -p recursion
• cargo check -q -p jolt-eval
• cargo check -q --features host
• cargo clippy --all --features host -q --all-targets -- -D warnings
• cargo clippy --all --features host,zk -q --all-targets -- -D warnings
• cargo nextest run -p jolt-prover-legacy muldiv --cargo-quiet --features host
• cargo nextest run -p jolt-prover-legacy muldiv --cargo-quiet --features host,zk

Posted by the assistant on behalf of Quang Dao using GPT-5.