inspect: resolve the judge once and pass it into runMultiAgentPath

Addresses a Trail review note about runMultiAgentPath re-deriving the judge and assuming success. The described crash couldn't occur (the provider assignment was guarded by the ok check, so it stayed nil, and composeMultiAgentSinks skips synthesis on a nil provider), but the validate-then-re-derive-and-assume pattern was fragile.

runReview now resolves the judge once, errors if none resolves, and passes the validated judgeSpec into runMultiAgentPath, which uses it directly. Single source of truth; no second derivation, no nil case.