Feature request: search/filter in the composer model picker (patch ready)

[g3noce]

Summary

The composer's model picker shows every model a provider advertises in one grouped list. With large catalogs that is a long scan; a live search field in the model-list pane would make choosing fast.

Proposed behavior

• Search field at the top of the model-list pane (the menu opened from the model seat next to the composer input).
• Filters the provider-grouped list as you type; a model matches on provider name/id and model name/id/description; groups with no surviving models disappear.
• A "no models match" message when nothing survives.
• The query resets whenever the menu reopens.

Implementation sketch

Adapted to packages/client/ui-model-selection (master) and running as a local patch on dsh web:

• src/client/ModelSelect.tsx — query state, filteredGroups/filteredCount memos, search input in the model pane, no-match empty state; query reset in show()/close().
• src/client/ModelSelect.module.css — .search field row (30px input row, existing board-surface tokens).
• src/client/locales.ts — search.placeholder / search.aria / search.noResults (zh + en).
• tests/model-select.client.spec.tsx — ModelSelect model search suite (filter by name/id/group/description, no-match message, reset on reopen).

Core filter:

const filteredGroups = useMemo(() => {
  const q = query.trim().toLowerCase()
  if (q === '') return state.groups
  return state.groups.map(group => ({
    ...group,
    models: group.models.filter(model =>
      `${group.name} ${group.id} ${model.name} ${model.id} ${model.description ?? ''}`
        .toLowerCase()
        .includes(q),
    ),
  })).filter(group => group.models.length > 0)
}, [state.groups, query])

The /model popup shares the same directory and could reuse the same filter as a follow-up. Happy to share the full patch or adjust matching/wording/perf behavior if this direction is interesting to the team.