Fix save_json to save files to lunar_json directory

- Add output_dir parameter (default: "lunar_json")
- Auto-create directory if not exists
- Update output message to show full file path

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

lunar_calendar.py

@@ -205,13 +205,17 @@ class LunarCalendar:
 
         return result
 
-    def save_json(self, filename: str | None = None):
+    def save_json(self, filename: str | None = None, output_dir: str = "lunar_json"):
         """將該年日曆輸出為 JSON 檔"""
+        import os
+
         data = self.build_calendar()
+        os.makedirs(output_dir, exist_ok=True)
         fname = filename or f"{self.year}.json"
-        with open(fname, "w", encoding="utf-8") as f:
+        filepath = os.path.join(output_dir, fname)
+        with open(filepath, "w", encoding="utf-8") as f:
             json.dump(data, f, ensure_ascii=False, indent=2)
-        print(f"完成！已輸出：{fname}")
+        print(f"完成！已輸出：{filepath}")
 
 
 if __name__ == "__main__":