fix(question_gen): gates reject_reason returns raw reason; short-circuit skips LLM

- GateReport.reject_reason now returns gate.reason directly (no [name] prefix)
- verbatim short-circuit sets other 3 gates to SKIP without calling LLM
- test_high_verbatim_shortcircuits asserts zero LLM calls and SKIP verdicts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/unit/test_gates.py

@@ -293,7 +293,7 @@ class TestRunGates:
 
     @pytest.mark.asyncio()
     async def test_high_verbatim_shortcircuits(self) -> None:
-        """verbatim_ratio > 0.5 → key_verify 直接 FAIL，不调用 LLM。"""
+        """verbatim_ratio > 0.5 → key_verify 直接 FAIL，其余 SKIP，不调用 LLM。"""
         llm = MockLLM([_make_llm_response("pass", "should not be called")])
         candidate = _make_candidate()
         tree = _make_tree()
@@ -310,3 +310,9 @@ class TestRunGates:
         assert report.passed is False
         assert report.key_verify.verdict == GateVerdict.FAIL
         assert "verbatim" in report.key_verify.reason.lower()
+        # 其余三门应为 SKIP
+        assert report.blind_answer.verdict == GateVerdict.SKIP
+        assert report.multi_true.verdict == GateVerdict.SKIP
+        assert report.leak_test.verdict == GateVerdict.SKIP
+        # LLM 不应被调用
+        assert len(llm.calls) == 0