feat: improve model provider presets and editing UX

[youngbeom-shin]

Summary

• add model provider presets and provider-specific avatars across create/detail/sidebar flows
• improve model provider create/edit UX for API key masking, validation, tooltip/modal styling, and zh-CN copy
• persist preset metadata and fix custom provider id/display-name handling, including unicode ids and duplicate-name edge cases

Validation

• pnpm --dir web/app typecheck
• pnpm --dir web/app exec vitest run tests/models/modelProviders.test.ts

Impact

• model provider creation, editing, sidebar rendering, and local config persistence