ui : polish the models page layout and filters
Give the models page a page header with the Discover action, calmer
column labels, tinted section and family headers, and an empty state.
Load the model list on a direct visit, slide the detail pane over the
table below xl, and draw the filter toggles as one box matching the
context select, with room for their shadow.
Assisted by: Claude (Opus 5.5 Medium)
