feat: display.txt 传递原子半径数组，draw.py 读取 per-atom 半径

之前所有原子使用统一的 ball_radius（来自 input.txt），
现在 display.txt header 包含 atom_radii 字段（逗号分隔
的半径数组），draw.py 据此为每个原子设置独立半径。
fallback：若没有 atom_radii 字段，仍使用 ball_radius。

compute.py

@@ -1460,7 +1460,8 @@ def run_simulation(save_trajectory=0):
                        "gravity_strength": str(GRAVITY_STRENGTH),
                        "driving_force": str(DRIVING_FORCE),
                        "use_marker": str(use_marker),
-                       "alpha": ",".join(str(a) for a in (alpha if isinstance(alpha, list) else [alpha]))}
+                       "alpha": ",".join(str(a) for a in (alpha if isinstance(alpha, list) else [alpha])),
+                       "atom_radii": ",".join(str(r) for r in ATOM_RADII)}
     )
     print(f"[compute] display.txt 已保存至: {disp_path} ({n_frames_actual} 帧)")