Let the CultNet contract drift guard pass on a clean tree

git grep exits 1 when it finds nothing, and the GitHub pwsh step wrapper
ends the step with that $LASTEXITCODE, so the guard failed on exactly the
clean tree it should accept. End the step with an explicit exit 0 after the
checks; a real drift still throws first.

REC-032.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.github/workflows/cultnet-interop.yml

@@ -87,6 +87,9 @@ jobs:
           if ($stray -or $oldNamespace) {
             throw "CultNet schema contracts drifted out of contracts/cultnet/ (REC-032). See CultLib/contracts/cultnet/ and rewrite any `$id back to https://github.com/GameCult/CultLib/contracts/cultnet/."
           }
+          # git grep exits 1 when nothing matches, and the runner's pwsh wrapper
+          # ends the step with that $LASTEXITCODE; a clean tree must pass.
+          exit 0
 
       - name: Install Node dependencies
         run: npm install --no-package-lock