Model picker search should match pasted model slugs

[tntuser77]

Pasting a model id into the model picker search finds nothing, even when the model is right there in the list. Concrete repro: an OpenCode instance with an OpenRouter key has openrouter/stealth/space-bunny-alpha in its catalog. Searching bunny finds it (display name "Space Bunny Alpha"). Pasting stealth/space-bunny-alpha finds nothing.

Why: getModelPickerSearchFields (apps/web/src/components/chat/modelPickerSearch.ts) indexes display name, short name, sub-provider, driver kind, and instance display name, but never the model slug. The scorer is tokenized and every token must match a field; fuzzy is a subsequence match, so a pasted slug dies on its / and - characters, which exist only in the slug and in no indexed field.

Proposal: index the model slug as one more search field, so pasting an id like stealth/space-bunny-alpha or openrouter/stealth/space-bunny-alpha surfaces the model. The picker row data already carries the slug. T3 slugs carry the driver provider prefix (the model above is openrouter/stealth/space-bunny-alpha on an OpenCode instance), but the prefix does not block a match: the includes tier of scoreQueryMatch (packages/shared/src/searchRanking.ts) treats the prefixless paste as a substring, and / is already a boundary marker there.

Looks like a small change to the search fields plus tests, no UX change otherwise. Happy to send a PR if maintainers want it.