Isaac Sim 6 USD assets

Self-contained Isaac Sim 6 USD packages for seven Franka robot families.
Each archive extracts to one <model>/ directory with closed, relative
references — open <model>/<model>.usda directly in Isaac Sim 6.0.0-rc.59.

• Mobile archives additionally embed worlds/sensor_test_world.usda
  (collision floor + colored camera/lidar targets).
• Sensor-bearing archives (franka_mobile_sensors,
  franka_vision_and_manipulation_kit,
  mobile_fr3_duo_with_vision_and_manipulation_kit) also embed
  worlds/sensorized_world.usda, declarative sensors/ profiles, and
  archive-local tools/ for native Camera / OmniLidar / IMU bootstrap and
  capture — see each archive's README.txt.
• tarball_manifest.json records the tar_sha256 and transport sha256
  of every archive; each archive also carries its own SHA256SUMS.