fix(test): stop overriding host-aware vitest scheduling in prepare gates

[hxy91819]

Summary

• The hardcoded OPENCLAW_VITEST_MAX_WORKERS=${OPENCLAW_VITEST_MAX_WORKERS:-4} default in gates.sh short-circuits the host-aware scheduling system introduced in c247e36
• resolveLocalVitestScheduling sees the explicit 4 and returns maxWorkers=4, which falls below the >= 5 threshold in shouldUseLargeLocalFullSuiteProfile, so every machine gets the DEFAULT profile (4 shard parallelism) instead of LARGE (10)
• Now only forwards OPENCLAW_VITEST_MAX_WORKERS when explicitly set by the user; otherwise lets test-projects.mjs detect host resources and pick the appropriate profile automatically

Test plan

• Verify on a machine with >= 12 cores / >= 48GB RAM that scripts/pr-prepare gates <PR> now prints parallelism 10 instead of parallelism 4
• Verify that setting OPENCLAW_VITEST_MAX_WORKERS=2 still correctly forwards the override
• Verify that CI behavior is unchanged (CI uses OPENCLAW_LOCAL_CHECK=0 and does not set OPENCLAW_VITEST_MAX_WORKERS)

[greptile-apps]

Greptile Summary

This PR removes the hardcoded OPENCLAW_VITEST_MAX_WORKERS=4 default in scripts/pr-lib/gates.sh, which was suppressing the host-aware vitest scheduling introduced in c247e36. The fix correctly conditionally forwards the env var only when explicitly set by the user, allowing test-projects.mjs to auto-detect host resources and apply the appropriate scheduling profile (LARGE for high-core/RAM machines, DEFAULT otherwise).

Confidence Score: 5/5

Safe to merge — single-file, targeted fix with no behavioral regression for CI or explicit-override users.

The change is a one-block conditional that only removes an unintended hardcoded default. The previous_full_gates_head assignment sits correctly outside the if/else, so gate state is preserved in both branches. No P0/P1 findings.

No files require special attention.

_{Reviews (1): Last reviewed commit: "fix(test): stop overriding host-aware vi..." | Re-trigger Greptile}