docs(voxtral_realtime): document CUDA Windows workflow

[larryliu0820]

Add CUDA-Windows instructions to the Voxtral Realtime README, including export prerequisites and an example command.

Document Windows build steps via CMake workflow presets and add PowerShell run examples with and without the .ptd data file.

Note recommended CUDA architectures for int4 kernels, and reformat voxtral_realtime CMake presets without changing behavior.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/17993

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❌ 4 New Failures, 12 Pending, 1 Unrelated Failure

As of commit cd423fc with merge base eb77ed4 ():

NEW FAILURES - The following jobs have failed:

• Lint / link-check / lint-xrefs (gh)
  Process completed with exit code 1.
• pull / test-binary-size-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 75ffe7149ecbed363d12f4fe8a307da1f1d9a1a7cccd20267bbf10fb0cc0bc33 /exec failed with exit code 1
• pull / test-binary-size-linux-gcc / linux-job (gh)
  RuntimeError: Command docker exec -t 5cb1541e8e5820c9a5fad65a1d9a5230049cf5a720b7cd835cff0c18607cbd93 /exec failed with exit code 1
• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / macos / macos-job (gh) (trunk failure)
  AttributeError: '_OpNamespace' 'mkldnn' object has no attribute '_is_mkldnn_acl_supported'

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