apr-cli: 65 #[contract] sites with no producer build.rs enforce nothing (#2699 remainder) #4370

Sub-issue of #2870 (P-1.1). Remainder of #2699, per cop scoping (aprender-77, 09:15Z 2026-09-25).

apr-cli has 65 #[contract] sites and no producer build.rs, so no CONTRACT_* env var reaches its compilation and every site expands to zero assertions. They are decorative.

done_when: apr-cli gets a producer, so its sites carry their YAML pre/postconditions, and it emits the registry sentinel. A site naming an unknown contract is a compile error. Otherwise each site is removed or re-targeted to a contract that exists. A count of sites with enforced conditions is reported before and after.