ui : model id grammar for sidecars, quants and capability parsing (#27946)

* ui : model id grammar for sidecars, quants and capability parsing

Extend the shared model id parser with sidecar tokens (draft variants and
auxiliary imatrix/mmproj files), weight-file and custom-quant regexes, and add
the tools capability to ModelCapabilities; the selector option row picks it up
from the model's declared capabilities.

Assisted-by: pi:GLM-5.3-Flash

* ui : escape sidecar tokens in the regex alternation

Assisted-by: pi:zai-org/GLM-5.3-Flash