docs(libero): commit side-by-side videos (compressed <500KB) + static frames

Fix 'video not working' on roboverse.wiki: *.mp4 is gitignored so the side-by-side
mp4s were never committed (404 on deploy). Force-add them, compressed to ~115KB
(h264/yuv420p, under the 500KB pre-commit limit, matching the repo's tracked doc
videos), plus an extracted side-by-side frame PNG as poster + always-visible
fallback (native LIBERO left | MetaSim right).

Author: geng-haoran

docs/source/_static/integrations/libero/sidebyside_dynamics_frame.png

@@ -108,27 +108,27 @@ Beyond "passthrough == native by construction", we load each task's own combined
 MJCF (Franka + objects + arena + camera) into **MetaSim's MuJoCo handler** and
 reproduce the demo — proving the MetaSim backend simulates the LIBERO scene 1:1.
 
-```{note}
-The videos play on the built docs site (roboverse.wiki). On GitHub's markdown
-viewer, inline `<video>` of a repo-relative file does not play — use the
-download links, or build the docs locally (`cd docs && make html`).
-```
+In each frame, **left = native LIBERO `agentview_rgb`, right = MetaSim render**.
+
+**Stage 1 — kinematics** (per-frame `set_states`, geometry/pose 1:1):
 
-**Stage 1 — kinematics** (per-frame `set_states`, geometry/pose 1:1) —
-[download](../../_static/integrations/libero/sidebyside_kinematic_spatial_task0.mp4):
+![Stage 1 side-by-side: native LIBERO (left) vs MetaSim (right)](../../_static/integrations/libero/sidebyside_kinematic_frame.png)
 
-<video controls width="640" preload="metadata">
+<video controls width="640" preload="metadata" poster="../../_static/integrations/libero/sidebyside_kinematic_frame.png">
   <source src="../../_static/integrations/libero/sidebyside_kinematic_spatial_task0.mp4" type="video/mp4">
 </video>
 
-**Stage 2 — dynamics** (MetaSim's engine steps under the captured ctrl) —
-[download](../../_static/integrations/libero/sidebyside_dynamics_spatial_task0.mp4):
+▶ [play / download the kinematic side-by-side video](../../_static/integrations/libero/sidebyside_kinematic_spatial_task0.mp4)
+
+**Stage 2 — dynamics** (MetaSim's engine steps under the captured ctrl):
+
+![Stage 2 side-by-side: native LIBERO (left) vs MetaSim engine (right)](../../_static/integrations/libero/sidebyside_dynamics_frame.png)
 
-<video controls width="640" preload="metadata">
+<video controls width="640" preload="metadata" poster="../../_static/integrations/libero/sidebyside_dynamics_frame.png">
   <source src="../../_static/integrations/libero/sidebyside_dynamics_spatial_task0.mp4" type="video/mp4">
 </video>
 
-Left = native LIBERO `agentview_rgb`, right = MetaSim render. Per-frame
+▶ [play / download the dynamics side-by-side video](../../_static/integrations/libero/sidebyside_dynamics_spatial_task0.mp4) Per-frame
 `max|qpos − recorded| = 0.0` (exact); the MetaSim engine step matches reference
 MuJoCo to `max|Δ| = 1.6e-4` (float accumulation). Residual pixel MAE ≈ 2.5–5/255
 is renderer config (lighting / anti-aliasing), not physics.