[Docker] Call the isaaclab console script directly in the images

[hujc7]

Summary

The Docker images call isaaclab.sh -p for every Python invocation. Putting the environment
on PATH makes the isaaclab console script directly callable, so the call sites read
isaaclab -p — shorter than the launcher path, with no wrapper.

Description

Follow-up to a review comment asking what it would take to remove isaaclab.sh -p from the
images:

#7405 — [Docker] Install the Docker images from uv.lock (merged)

• ENV PATH="${VENV_PATH_ARG}/bin:${PATH}" — placed below the install layers, which it
  would otherwise invalidate. Nothing is shadowed: python3, pip3 and isaaclab are not on
  PATH in the current images at all.
• uv run was the alternative and needs --frozen --no-sync --project to behave the same:
  without them it re-resolves the project on every call and warns when invoked outside it.
  Measured 124 ms against 110 ms per call, for a longer line.
• install_deps.py apt moves below the workspace install. It ran before it, where the
  console script cannot import its own package. Nothing between the two steps needs apt
  first — the third-party packages are already installed and the workspace members are
  pure-Python editables.
• Two aliases removed — isaaclab shadowed the console script once it is on PATH, and
  tensorboard was an explicit path into the environment.

isaaclab.sh still ships and is unchanged; this only changes how the images reach it.

Type of change

• New feature (non-breaking change which adds functionality) — the images gain isaaclab on
  PATH; no public API changes

Release backport

• Backport this pull request to the active release branch after it merges into develop

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• No documentation change is required — the documented isaaclab.sh entrypoint still ships and is unchanged
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works — built base and cuRobo and verified isaaclab -p imports isaacsim, the prebundle repoint still runs, and no prebundled package is left dangling
• A changelog fragment is not required because no source package changed — the diff is docker/ only
• I have added my name to the CONTRIBUTORS.md or my name already exists there