ui : reuse the canonical quant bit-depth and extension parsing
Drop the duplicated UD- prefix and quant bit-depth regexes from the download
options utils: quantBitDepth re-implemented, more crudely, what
HuggingFaceService.getBitDepth already does, and the label helper re-declared
the weight-extension pattern held by MODEL_ID. The command preview now derives
its bit depth via the service, so the quant chips and the command sorts agree.
Assisted-by: llama-ui:Qwen3.8-Flash-Next