fix(tests): venue-parity interface probes must not pipe into grep -q

[DeusData]

What

The two layer-5 interface probes in tests/test_venue_parity_contract.sh tested for a substring by piping captured output into grep -q. Under set -o pipefail that converts a satisfied contract into a probe failure.

Why it fails

grep -q exits at the first match. If the payload exceeds the pipe buffer, the writer takes EPIPE on the remainder, and pipefail surfaces the writer's non-zero status — even though the match succeeded.

Observed on macos-15-intel:

test_venue_parity_contract.sh: line 404: printf: write error: Broken pipe
INTERFACE CONTRACT: scripts/ci/smoke-artifact.sh --help must exit 0 and print a Usage: block (rc=0)
VENUE PARITY CONTRACT VIOLATED — interface probes failed (layer 5)

Note rc=0, and the Usage: block was present — the successful match is exactly what made grep exit early. smoke-artifact.sh --help is 698 bytes against a 512-byte PIPE_BUF and prints Usage: on its first line, so the writer is killed at the earliest possible moment. Whether its remaining write lands before grep exits is a scheduling race — hence a single-runner "flake" that is really a harness defect.

Fix

Both pipelines become in-shell case matching: no subprocess, no pipe, no race. The second probe also becomes a strictly literal match (its "Please consult --help." was previously a regex whose . matched any character).

Verification

• Contract passes: venue-parity contract OK / interface probes OK (18 --help entries, 8 strict-flag entries).
• Negative control: the matcher still yields "absent" for output with no Usage: block, so the probe can still fail. A gate that cannot fail would be worse than a flaky one.