docs: case05纵波 + case06横波一维原子链

- case05 Readme.md 更新为纵波模拟描述
- case05 run_dynamics.py 注释更新
- case06 创建为一维原子链横波模拟
  - coord.txt: fix_x=1, fix_y=1, fix_z=0 (z方向自由)
  - driver.txt: amp_z=0.5, freq_z=0.1, phi_z=90°
  - input.txt: 横波配置 + step_plot_wave
  - Readme.md + doc/index.html + run_dynamics.py
- 模拟验证通过 (50000步/30s)

plot_wave.py

@@ -234,19 +234,38 @@ def plot_wave(output_dir):
 
     ani = FuncAnimation(fig, update, frames=n_frames, interval=50, blit=True)
 
-    # 保存 GIF
+    # ── 先输出 GIF（自动循环）──
     gif_path = os.path.join(output_dir, "wave_animation.gif")
     ani.save(gif_path, writer="pillow", fps=min(20, max(1, n_frames // 5)))
     print(f"[plot_wave] GIF 已保存: {gif_path}")
 
-    # 尝试保存 MP4
+    # ── 再输出 MP4（需要 ffmpeg）──
     try:
-        mp4_path = os.path.join(output_dir, "wave_animation.mp4")
-        ani.save(mp4_path, writer="ffmpeg", fps=min(20, max(1, n_frames // 5)))
-        print(f"[plot_wave] MP4 已保存: {mp4_path}")
-    except Exception:
-        pass
+        import matplotlib.animation as manim
+        import matplotlib.pyplot as _plt
 
+        # 尝试通过 imageio_ffmpeg 定位 ffmpeg
+        ffmpeg_path = None
+        try:
+            import imageio_ffmpeg
+            ffmpeg_path = imageio_ffmpeg.get_ffmpeg_exe()
+        except Exception:
+            pass
+        if ffmpeg_path and os.path.exists(ffmpeg_path):
+            _plt.rcParams['animation.ffmpeg_path'] = ffmpeg_path
+
+        ffps = min(20, max(1, n_frames // 5))
+        writer = manim.FFMpegWriter(fps=ffps, codec="libx264",
+                                     extra_args=["-pix_fmt", "yuv420p"])
+        mp4_path = os.path.join(output_dir, "wave_animation.mp4")
+        ani.save(mp4_path, writer=writer)
+        print(f"[plot_wave] MP4 已保存: {mp4_path}")
+    except FileNotFoundError:
+        print("[plot_wave] 警告: 未找到 ffmpeg，跳过 MP4 输出")
+    except Exception as e:
+        print(f"[plot_wave] 警告: MP4 输出失败 ({e})，跳过")
+
+    # ── 最后显示动画窗口 ──
     plt.show()
     return gif_path