Re-enable antigravity review in gha + ai-config once quota is restored

[d-morrison]

Antigravity's model API returned HTTP 503 "high demand" / out-of-quota errors, failing the review / antigravity-review check on PRs. Per a maintainer request (2026-08-06), the caller workflow was disabled for now in the two repos that run it:

repo	workflow	id	state
Morrison-Lab/gha	.github/workflows/antigravity-review.yml	327572671	disabled_manually
Morrison-Lab/ai-config	.github/workflows/antigravity-review.yml	328000031	disabled_manually

ai-code-review.yml (the multi-agent selector) defaults its agents input to claude, gemini, so it does not route to antigravity and was left untouched.

Re-enable when quota returns

gh workflow enable 327572671 --repo Morrison-Lab/gha
gh workflow enable 328000031 --repo Morrison-Lab/ai-config

Verify with gh api repos/<repo>/actions/workflows/<id> --jq .state (should read active).