[Doc] Align environment variable docs with runtime envs

[Lidang-Jiang]

Summary

• Document every environment variable exposed by vllm_kunlun.platforms.envs
• Remove the stale FUSED_QK_ROPE_OP entry, which is not parsed by the runtime env module
• Add focused unit tests for env parsing and doc/runtime consistency

Before

Command run on origin/main with the new regression test copied into a temporary worktree:

PYTHONWARNINGS=ignore PYTHONPATH=$PWD pytest -q tests/ut/test_platform_envs.py

........................................................................ [ 94%]
...F                                                                     [100%]
=================================== FAILURES ===================================
_______________ test_documented_env_vars_match_runtime_env_vars ________________

    def test_documented_env_vars_match_runtime_env_vars():
        doc_path = (
            Path(__file__).resolve().parents[2]
            / "docs/source/user_guide/configuration/env_vars.md"
        )
        doc = doc_path.read_text()
    
        for name in envs.__dir__():
>           assert f"`{name}`" in doc
E           AssertionError: assert '`VLLM_MULTI_LOGPATH`' in '# Environment Variables\n\nvllm-kunlun uses the following environment variables to configure the system:\n\n| *Enviro...oPE implementation\\****. Default is `0` (use original/standard RoPE). Setting to `1` may be used to enable QWEN3. |\n'

tests/ut/test_platform_envs.py:79: AssertionError
=========================== short test summary info ============================
FAILED tests/ut/test_platform_envs.py::test_documented_env_vars_match_runtime_env_vars
1 failed, 75 passed in 1.74s

After

PYTHONWARNINGS=ignore PYTHONPATH=$PWD pytest -q tests/ut/test_platform_envs.py

........................................................................ [ 94%]
....                                                                     [100%]
76 passed in 1.73s

ruff check tests/ut/test_platform_envs.py

All checks passed!

PYTHONWARNINGS=ignore black --target-version py310 --check tests/ut/test_platform_envs.py

All done! ✨ 🍰 ✨
1 file would be left unchanged.

git diff --check

(no output; exit code 0)

PYTHONWARNINGS=ignore pre-commit run --files docs/source/user_guide/configuration/env_vars.md tests/ut/test_platform_envs.py

fix end of files.........................................................Passed
trim trailing whitespace.................................................Passed
check yaml...........................................(no files to check)Skipped
check toml...........................................(no files to check)Skipped
check for added large files..............................................Passed
ruff check...............................................................Passed
isort....................................................................Passed
black....................................................................Passed
PyMarkdown...............................................................Passed
Lint GitHub Actions workflow files...................(no files to check)Skipped
Check for spaces in all filenames........................................Passed
Suggestion...............................................................Passed
- hook id: suggestion
- duration: 0s

To bypass pre-commit hooks, add --no-verify to git commit.

Test plan

• PYTHONWARNINGS=ignore PYTHONPATH=$PWD pytest -q tests/ut/test_platform_envs.py
• ruff check tests/ut/test_platform_envs.py
• PYTHONWARNINGS=ignore black --target-version py310 --check tests/ut/test_platform_envs.py
• git diff --check
• PYTHONWARNINGS=ignore pre-commit run --files docs/source/user_guide/configuration/env_vars.md tests/ut/test_platform_envs.py