Use natural sorting for model names.
Previously the model list was sorted lexicographically, which resulted
in unintuitive ordering when numbers were included in the name.
Example:
Before
qwen3.5:2B
qwen3.5:35B-3AB
qwen3.5:9B
After
qwen3.5:2B
qwen3.5:9B
qwen3.5:35B-3AB
This change sorts models using natural order so numeric parts are
compared numerically.
