fix(ci): update math vault evaluations to use recursive grep, resolving exit code 2

Author: jtrag

.github/workflows/prompt-evals.yml

@@ -19,4 +19,4 @@ jobs:
       - uses: actions/checkout@v4
       - name: Math Stability Audit
         run: |
-          grep -i "TTT\|TUPT\|LWE" .github/prompts/
+          grep -ri "TTT\|TUPT\|LWE" .github/prompts/