t27b: refuse signed % on an untyped local, as the reference does (verify_multitarget) #6593

After #6584, verify_multitarget.t27 compiles under t27b and fails, while the reference (t27c gen-zig + zig test) refuses it, because of a signed % on an untyped local. t27b should refuse it at the same stage, so the verdicts agree.

Refs #6063.

Success Criteria

• A conformance spec under specs/tri/t27b/conformance/ with a signed % on an untyped local is refused by t27b with a typed reason.
• verify_multitarget moves from fail to blocked in the lab, and reference_disagree stays 0.

Boundary

• specs/port/tools/verify_multitarget.t27

User Scenarios

• Given a t27 spec containing a signed % operation on an untyped local variable, when t27b compiles it, then t27b refuses compilation with a typed reason at the same stage as the reference compiler.

Requirements

• FR-001: t27b MUST reject a signed % on an untyped local during type checking with a typed diagnostic.
• FR-002: The rejection MUST occur at the same compilation stage as the reference (t27c gen-zig + zig test) so that verdicts agree.

Success Criteria

• t27b specs/port/tools/verify_multitarget.t27 exits with non-zero and emits a typed error about signed % on untyped local.
• A new conformance spec under specs/tri/t27b/conformance/ containing a signed % on an untyped local is refused by t27b with a typed reason (exit 0 for the test runner asserting refusal).
• verify_multitarget moves from fail to blocked in the lab, and reference_disagree stays 0 (measured by lab metrics).