feat: DuckDB quantiles in-process (gcc CGO), not Ladybug. (#34)

OQ3: internal/duckstats + bin/qa/stats.go. Zig stays Ladybug-only.
mikefarah/yq for small structured slices. Gitea #30.

bin/tools/test_system_perf.py

@@ -0,0 +1,36 @@
+"""qa/system_perf.py is an offline-gated system test (no live brain in CI)."""
+from __future__ import annotations
+
+import ast
+import unittest
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[2]
+
+
+class SystemPerfScriptTest(unittest.TestCase):
+    def test_script_compiles_and_is_read_only(self) -> None:
+        path = ROOT / "qa" / "system_perf.py"
+        src = path.read_text()
+        compile(src, str(path), "exec")
+        self.assertIn("--json", src)
+        self.assertIn("qwen3.5:9b", src)
+        self.assertIn("--picoclaw", src)
+        self.assertIn("BRAIN_URL", src)
+        self.assertIn("tools/list", src)
+        self.assertIn("tools/call", src)
+        self.assertIn("GATE_HEALTH_MS", src)
+        self.assertIn("GATE_GET_P50_MS", src)
+        self.assertNotIn("kb.lbug", src)
+        self.assertNotIn("password", src.lower())
+        self.assertNotIn("token", src.lower())
+
+    def test_script_does_not_write_ladybug(self) -> None:
+        tree = ast.parse((ROOT / "qa" / "system_perf.py").read_text())
+        writes = [
+            n.func.attr
+            for n in ast.walk(tree)
+            if isinstance(n, ast.Call) and isinstance(n.func, ast.Attribute)
+            and n.func.attr in {"write_text", "write_bytes", "dump"}
+        ]
+        self.assertEqual(writes, [], f"system_perf must not write files: {writes}")