Removes modular installation commands from docs

[kellyguo11]

Description

Updates documentation to clean up modular installation commands as they are not fully functional yet.

Type of change

• Documentation update

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[greptile-apps]

Greptile Summary

This PR cleans up Isaac Lab documentation by removing modular/partial installation commands that are not yet fully functional, simplifying the install story to the recommended full-bundle path.

Key changes:

• src_build_isaaclab.rst: Removes per-RL-framework and per-submodule install examples; replaces the block with a single sentence clarifying that --install installs everything.
• isaaclab_pip_installation.rst: Removes the extras table and all partial pip install variants (Isaac Lab only, individual sub-packages); only the full isaaclab[isaacsim,all] bundle command remains.
• quickstart.rst: Removes the explicit CUDA-enabled PyTorch install step and marks the Isaac Sim install as (Optional) — which creates a potential documentation gap (see inline comment).

The first two files are clean improvements. The quickstart change warrants a second look: now that Isaac Sim is framed as optional, the guide no longer tells users who skip Isaac Sim how to obtain a CUDA-enabled PyTorch build, which every RL framework depends on.

Confidence Score: 4/5

• Safe to merge with one minor documentation gap worth addressing before publication.
• All three files are documentation-only changes with no code impact. The removals in src_build_isaaclab.rst and isaaclab_pip_installation.rst are clean and correct. The only concern is in quickstart.rst: removing the PyTorch install step while simultaneously marking Isaac Sim as Optional leaves users who skip Isaac Sim without guidance on obtaining PyTorch — a likely install-failure path. This is a documentation clarity issue rather than a correctness bug, hence a score of 4 rather than 5.
• docs/source/setup/quickstart.rst — removal of PyTorch install step combined with the new "(Optional)" Isaac Sim label may leave a documentation gap for users who skip Isaac Sim.

Important Files Changed

Filename	Overview
docs/source/setup/installation/include/src_build_isaaclab.rst	Cleanly removes the modular per-framework / per-submodule install examples and replaces them with a single explanatory sentence; no issues.
docs/source/setup/installation/isaaclab_pip_installation.rst	Removes the extras table and partial-install pip commands; only the recommended full bundle command (isaaclab[isaacsim,all]) remains. Clean and consistent.
docs/source/setup/quickstart.rst	Removes the explicit CUDA PyTorch installation step and marks Isaac Sim as Optional, potentially leaving users who skip Isaac Sim without guidance on installing PyTorch.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Create virtual environment] --> B[Update pip]
    B --> C{Install Isaac Sim?\nOptional}
    C -- Yes --> D["uv pip install isaacsim[all,extscache]"]
    C -- No --> E["⚠️ PyTorch not installed\n(no longer documented here)"]
    D --> F[Clone Isaac Lab repo]
    E --> F
    F --> G["./isaaclab.sh --install\n(installs all sub-packages)"]
    G --> H[Run training scripts]

    subgraph pip_path["Pip Package Path (isaaclab_pip_installation.rst)"]
        P1["uv pip install 'isaaclab[isaacsim,all]'"] --> P2[Install PyTorch CUDA]
        P2 --> P3[Run user scripts]
    end

Loading

_{Last reviewed commit: 1cfb752}

[greptile-apps]

Missing PyTorch install step after making Isaac Sim optional

Before this PR the Isaac Sim install was unconditional, so PyTorch was always pulled in as a dependency. Now that the line reads "(Optional)", a user who skips the Isaac Sim step will find no instruction to install PyTorch anywhere in this guide — yet every RL framework (rl_games, rsl_rl, skrl, etc.) requires it.

The PR also removed the explicit CUDA-enabled PyTorch install command that used to appear just before this section:

uv pip install -U torch==2.10.0 torchvision==0.25.0 --index-url https://download.pytorch.org/whl/cu128

If the intent is that ./isaaclab.sh --install handles PyTorch automatically (or that users can rely on Isaac Sim bringing it in), it would be worth adding a short note here. For example:

Suggested change

	and now we can install the Isaac Sim packages (Optional).
	and now we can install the Isaac Sim packages (Optional). If you skip this step, install
	a CUDA-enabled PyTorch build manually before running ``isaaclab.sh --install``
	(see the :ref:`pip-installation` guide for the recommended command).

Without any such guidance, users on the Newton-only kitless path who still want to use RL frameworks will hit confusing import errors.