## Summary
- Replace the Link previews and Thread layout dropdowns with the shared
segmented control from #5644.
- Pair each setting with a real, inert preview: production Compact/Rich
link cards and a simplified Focus/Split thread diagram.
- Keep scrub previews local to Settings so only a completed selection
updates the saved preference and real app behavior.
- Keep each setting and preview responsive as one grouped unit, with
focused light/dark and narrow/wide coverage.
## Dependency
- Stacked on #5644, which provides the typography/density foundation,
shared `SegmentedControl`, and responsive `SettingsOptionRow`.
- After #5644 merges, this PR should be retargeted/rebased onto `main`.
## Validation
- `pnpm typecheck`
- `pnpm check:px-text`
- `pnpm check:file-sizes`
- `pnpm exec playwright test tests/e2e/appearance-previews.spec.ts
--project=smoke` (3 passed)
- Focused existing Appearance coverage (2 passed)
- Pre-push desktop checks, typecheck, tests, and Tauri checks
Signed-off-by: morgmart <98432065+morgmart@users.noreply.github.com>
