fix(test): update effort_validation test to accept low and max levels

The test's invalid-values list included "low" which was valid before
this PR but is now a legitimate effort level. Replace with "lowest"
(still invalid) so the test keeps its coverage without false-failing.

hive-ag3nt/src/events.rs

@@ -1271,7 +1271,7 @@ mod tests {
         }
         // Out-of-set, empty, and wrong-case inputs are rejected so a bad
         // picker POST never reaches `claude --effort`.
-        for bad in ["low", "", "MEDIUM", "ultra", "high "] {
+        for bad in ["lowest", "", "MEDIUM", "ultra", "high "] {
             assert!(!is_valid_effort(bad), "{bad:?} should be rejected");
         }
     }