Add QF_S string solver benchmark agentic workflow

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

.github/workflows/qf-s-benchmark.md

@@ -0,0 +1,38 @@
+---
+description: Run Z3 string solver benchmarks (seq vs nseq) on QF_S test suite from the c3 branch and post results as a GitHub discussion
+
+on:
+  schedule: weekly
+  workflow_dispatch:
+
+permissions: read-all
+
+network: defaults
+
+tools:
+  bash: true
+  github:
+    toolsets: [default]
+
+safe-outputs:
+  create-discussion:
+    title-prefix: "[QF_S Benchmark] "
+    category: "Agentic Workflows"
+    close-older-discussions: true
+  missing-tool:
+    create-issue: true
+
+timeout-minutes: 90
+
+steps:
+  - name: Checkout c3 branch
+    uses: actions/checkout@v5
+    with:
+      ref: c3
+      fetch-depth: 1
+      persist-credentials: false
+
+---
+
+<!-- Edit the file linked below to modify the agent without recompilation. Feel free to move the entire markdown body to that file. -->
+@./agentics/qf-s-benchmark.md