Add UVC32 wrist camera and refresh shared RS/DM assembly previews

[Yang-Ci]

Adds 32×32 UVC as the fourth shared B601-RS/B601-DM wrist camera assembly and replaces the four wrist-camera previews in all five official READMEs with MuJoCo assembly screenshots.

The UVC bracket is generated from the official UVC32_mount.step. Its camera-board mounting plane and 28×28 mm hole spacing are extracted from CAD; the clamp is aligned with the existing B601 attachment using the official D435 reference CAD. The camera board and lens are explicitly documented as generic simulation schematics, because the source STEP contains only the bracket. Optical pose and simulation FOV are nominal, not physical-device calibration.

The new Rebot_Arm_description/Camera/ resources include the URDF, generated STL meshes, original STEP files, deterministic CAD generator, updated Xacro expansion script, source hashes and a UVC MuJoCo screenshot. Chinese/English documentation covers all four variants and RS/DM attachment-frame differences. The web and ROS MuJoCo simulators use the same four-camera assets in ReBot_Arm_DigitalTwin_RS; assets are also synchronized to Rebot_Arm_description.

Validation:

• Four-model browser switching, persistence, ghost target, mobile layout and failure recovery passed; switching emitted no motion commands and preserved joint/TCP/gripper state.
• Native ROS selector → parameter → MuJoCo viewer → wrist RGB/CameraInfo synchronization passed for all four models, including C-key cycling and a late-starting renderer.
• Existing MuJoCo camera tests passed: 5 tests, including all four optical-frame transforms and simulation-state preservation.
• Verified all 25 source and 5 generated asset hashes; CAD regeneration is byte-identical.
• Verified URDF mesh references and documentation image/file paths.
• README translation checker and its 9 tests passed.
• git diff --check passed.

The existing Chinese/Japanese contact addresses are now explicit mailto: links to fix the six repository-wide link-check errors reported on the previous camera PR; addresses and contact names are unchanged.