Preserve auto-review model settings

[SergeSerb2]

Summary

• Preserve auto-review model selections as complete values while stripping defaults before persistence.
• Prevent an unchanged default provider ID from being removed when only the review model changes, which previously caused schema encoding to surface as a settings write-file failure.
• Add an end-to-end regression covering the persisted settings.json shape.

Area

• apps/mac — native macOS app
• apps/windows — Windows desktop app
• apps/mobile — iPhone companion app
• apps/server — backend server
• Shared packages (packages/contracts, packages/shared, packages/client-runtime, …) or relay (infra/relay)
• Build, CI, or release tooling
• Docs

Verification

• pnpm run verify --all passes (check + typecheck + tests; adds lint:mobile and the Swift suite)
• pnpm run test:mac passes (run by the full verification gate)
• Manually verified (describe below)

Focused regression: vp test run src/serverSettings.test.ts (18 tests passed).

Screenshots / Recordings

Not applicable; persistence-only fix with no UI changes.

Release notes

Fixed changing the auto-review model from macOS Settings.