fix(review): add 'none' strength for guards that produce no stdout output

A guard returning an empty dict (no stdout) was classified as 'soft',
causing test_works_as_is_hooks_have_soft_or_better to pass even for
a completely non-functional guard. Introduce 'none' strength when
result is empty so the meta-test correctly detects inactive guards.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Trecek

tests/execution/backends/test_hook_deny_efficacy_probe.py

@@ -285,7 +285,9 @@ def test_probe(
         hook_output = result.get("hookSpecificOutput", {})
         decision = hook_output.get("permissionDecision")
 
-        if decision == "deny":
+        if not result:
+            strength = "none"
+        elif decision == "deny":
             strength = "hard"
         else:
             strength = "soft"