feat(rn): [P0] Models settings page

[liuyidi]

Summary

Settings page to view/activate platform models and presets (no BYOK / Providers panel yet).

WebUI reference

• webui/src/pages/settings/models/ModelsSettings.tsx
• webui/src/pages/settings/models/useModelsSettings.ts
• webui/src/pages/settings/models/ModelsSettingsPage.tsx

API

• GET /api/settings
• POST /api/settings/platform-models/{id}/activate
• POST /api/settings/model-configurations/{id}/activate

RN landing

• New: src/app/settings/models.tsx
• Register in src/app/settings/_layout.tsx
• Entry from src/app/(tabs)/me.tsx
• i18n: src/lib/i18n/messages.ts

Acceptance

• Me → Models → list selectable
• Activate updates bootstrap / modelName

Depends

• chore: Settings API thin wrapper