Detect CUDA UMD Version from newer nvidia-smi output (fixes #5812) (#5817)

* Detect CUDA UMD Version from newer nvidia-smi output (#5812)

Newer NVIDIA drivers (e.g. 610.x on Windows) print the driver's max
CUDA capability as "CUDA UMD Version: X.Y" instead of the legacy
"CUDA Version: X.Y" header.  The installers and Studio setup scripts
were only matching the legacy spelling, so on a fresh RTX 5090
laptop with a 13.x driver they failed to detect any CUDA version
and fell through to the cu126 wheel default.

Accept both spellings everywhere we parse nvidia-smi output:

- install.ps1: Get-TorchIndexUrl regex now allows " UMD"
- install.sh: two-expression sed (POSIX BRE has no "?"); the two
  patterns are mutually exclusive per line, head -1 picks the match
- studio/setup.ps1: Get-PytorchCudaTag and the $DriverMaxCuda
  detector both relaxed
- studio/install_llama_prebuilt.py: substring scan replaced with a
  regex search using the same pattern
- tests/sh/test_get_torch_index_url.sh: new make_mock_smi_umd helper
  plus three UMD cases (13.3 -> cu130, 12.8 -> cu128, 11.8 -> cu118);
  all 30 tests pass locally

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