RoboLab v0.2.0

Added

• IsaacSim 5.1 / IsaacLab 2.3 support alongside 5.0 / 2.2, selected via the
  mutually-exclusive isaac50 / isaac51 extras.
• Relative differential-IK environment registrations
  (examples/run_rel_ik_demo.py).
• Realtime/pathtracing RTX renderer selection via --rendering-type.
• Poly Haven attribution files for the curated backgrounds.

Changed

• Bundled backgrounds trimmed to a curated indoor set. More backgrounds can be obtained from Poly Haven.
• End-effector pose position is recorded in the env-local frame.
• Docs: asset contribution guidelines, conditionals
  restructure; generalized VRAM sizing guide.

Fixed

• HDF5 episode success is derived from terminated rather than a named
  termination term.