[kreneskyp]

IR-881 CG consumer

Contract IR merged the STD-001 rename to kani_checker_absent. This PR updates CG's terminal map and owning spec to consume that name without an alias. UnavailabilityCause::SolverAbsent remains CG's distinct terminal settlement; the registered IR code and every reference to its former spelling are replaced.

The lockfile changes only quire-contract-ir and quire-contract-model to the same merged source revision. The selective Cargo update initially refreshed four unrelated transitive Git crates; each was restored through cargo update --precise. The RT revision remains 3cc88c48, and filament-core-data is unchanged.

Verification

• Spec-first, then red-test commits: the focused TC-041 test failed compilation because the old IR lock lacked KANI_CHECKER_ABSENT.
• Implementation commit: focused TC-041 test passed against the selectively updated IR lock.
• Mutation control: temporarily mapped KANI_BACKEND_ABSENT in the checker arm. TC-041 failed with Unsupported(BackendAbsent) instead of Unsupported(SolverAbsent); source restored and the worktree is clean.
• Pre-PR RUST_TEST_THREADS=1 QSPEC_DIR=/home/peter/dev/quire-specification make ci passed on exact head 3f06f98f: both MSRV and regular passes completed 378 unit, 665 integration and 16 doc tests. The real Kani gate passed 37/37 with a clean tree, and make cargo-audit passed with one allowed yanked-crate warning. The serial setting avoids a separately tracked stand-in startup ceiling flake observed under parallel full-suite load; its isolated test also passed.

Independent code/Rust, gap and spec review is required before merge. Final full gates will run again on the reviewed head.