fix(settings): align model picker and restore metadata text

[bobleer]

Summary

• stretch the Combobox and MultiSelect search field to the full popover width
• replace corrupted Unicode replacement characters in model settings with intentional separators, ellipses, and empty-state dashes
• add regression coverage for both presentation contracts

Verification

• pnpm --dir src/web-ui run test:run src/infrastructure/config/components/ModelSettingsPage.presentation.test.ts
• node --test design-system/packages/ui/tests/combobox.test.mjs
• pnpm run check:web
• pnpm run design-system:check
• pnpm run check:repo-hygiene

Remote scenarios

• not exercised; these changes are presentation-only and do not alter remote workspace, remote control, peer-device, or detached-dispatch behavior