Added UMI-Gripper

Author: omarrayyann

.DS_Store

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+## UMI-Gripper Description (MJCF)
+
+> Requires MuJoCo 2.2.2 or later.
+
+### Overview
+
+This package contains a simplified robot description (MJCF) of the [Universal Manipulation Interface (UMI) Gripper](http://umi-gripper.github.io/). It is derived from the publicly available [CAD model](https://docs.google.com/document/d/1TPYwV9sNVPAi0ZlAupDMkXZ4CA1hsZx7YDMSmcEy6EU/edit?tab=t.0).
+
+[URDF description](https://github.com/pal-robotics/talos_robot/tree/kinetic-devel/talos_description).
+
+<p float="left">
+  <img src="umi_gripper.png" width="600px">
+</p>
+
+
+###  -> URDF derivation step
+
+1. 
+
+### URDF -> MJCF derivation step
+
+1. Added `<mujoco> <compiler balanceinertia="true" discardvisual="false"/> </mujoco>` to the URDF's `<robot>`clause in order to preserve visual geometries.
+2. Loaded the URDF into MuJoCo and saved a corresponding MJCF.
+3. Updated the `<compiler>` tag in the MJCF to specify `meshdir="assets/"` and `texturedir="assets/"` for correct asset loading.
+4. Added materials and textures for the mirrors and ArUco markers (`right_aruco_sticker.png`, `left_aruco_sticker.png`).
+5. Created a `<default>` section to define common properties for joints, actuators, and geoms.
+6. Added two mirror geoms (`left_mirror`, `right_mirror`) with reflective materials for enhanced visual effects.
+7. Defined left and right finger holders with appropriate inertial properties and joints (`finger_left_joint`, `finger_right_joint`).
+8. Introduced a `<tendon>` section with a fixed tendon named split to synchronize the movement of both fingers.
+9. Added position-controlled actuators for the fingers and gripper joints.
+10. Tuned contact parameters by setting `impratio="10"` for better non-slip interaction.
+11. Added `scene.xml` which includes the robot, with a textured groundplane, skybox, and haze.
+
+### License
+
+This model is released under an [Apache-2.0 License](LICENSE).