Make scalar Flux predicates load-bearing at their call sites

[arniber21]

What to build

Turn the existing boolean reification proofs for bounds, arity, linearity, and schedule ordering into contracts that protect the operations relying on them. A proof that a helper returns the comparison in its body is not sufficient unless the refined fact reaches construction or indexing.

Acceptance criteria

• QASM index and gate-arity validation produce validated IDs/gates whose later use needs no repeated unchecked indexing.
• Linearity boundary predicates feed the IR verifier result rather than existing only as standalone equivalence proofs.
• Schedule monotonicity and wait-barrier predicates are used by the authoritative schedule validator under Flux checking.
• Decorative predicate specs with no proof-consuming caller are removed or replaced by refined constructors.
• Negative compile fixtures demonstrate Flux rejects one bounds, arity, linearity, and ordering violation.
• Stable runtime validation behavior remains unchanged for builds without Flux.

Blocked by

• Restore complete and deterministic Flux CI coverage #404

[arniber21]

Implemented and merged via PR #458. Closing as complete.