fix: _parse_llm_response now handles empty/invalid JSON gracefully

test: add gap coverage tests (hina_agent/JCL/quality gate edge cases)

hina/hina_agent.py

@@ -151,8 +151,11 @@ def _parse_llm_response(raw: str) -> dict:
         end = text.index("```", start) if "```" in text[start:] else len(text)
         text = text[start:end].strip()
 
-    parsed = json.loads(text)
-    return _validate_result(parsed)
+    try:
+        parsed = json.loads(text)
+        return _validate_result(parsed)
+    except (json.JSONDecodeError, ValueError):
+        return _validate_result({})
 
 
 def _validate_result(parsed: dict) -> dict: