feat: 摄像机初始位置可在 input.txt 配置

新增 input.txt 字段：
  camera_distance:  40.0   # 到场景中心的距离
  camera_elevation: 0      # 俯仰角
  camera_azimuth:   0      # 方位角

通过 display.txt header 传递到 draw.py，
不再硬编码在 draw.py 中。

compute.py

@@ -1461,7 +1461,10 @@ def run_simulation(save_trajectory=0):
                        "driving_force": str(DRIVING_FORCE),
                        "use_marker": str(use_marker),
                        "alpha": ",".join(str(a) for a in (alpha if isinstance(alpha, list) else [alpha])),
-                       "atom_radii": ",".join(str(r) for r in ATOM_RADII)}
+                       "atom_radii": ",".join(str(r) for r in ATOM_RADII),
+                       "camera_distance": str(config.get("camera_distance", 40.0)),
+                       "camera_elevation": str(config.get("camera_elevation", 0)),
+                       "camera_azimuth": str(config.get("camera_azimuth", 0))}
     )
     print(f"[compute] display.txt 已保存至: {disp_path} ({n_frames_actual} 帧)")