test: add unit test coverage for invalid_history_count and unknown_option classifier arms

Two classifier arms had no corresponding assert_eq! in
test_classify_error_kind_returns_correct_discriminants: invalid_history_count
(both prefix and contains paths) and unknown_option (#790). Now 49/39 = full
coverage of all classify_error_kind return values.

rust/crates/rusty-claude-cli/src/main.rs

@@ -13259,6 +13259,20 @@ mod tests {
             ),
             "invalid_resume_argument"
         );
+        // coverage: invalid_history_count arm
+        assert_eq!(
+            classify_error_kind("invalid_history_count: abc is not a valid count"),
+            "invalid_history_count"
+        );
+        assert_eq!(
+            classify_error_kind("something invalid count something"),
+            "invalid_history_count"
+        );
+        // coverage: unknown_option arm (#790)
+        assert_eq!(
+            classify_error_kind("unknown_option: unknown system-prompt option: --foo."),
+            "unknown_option"
+        );
     }
 
     #[test]