Port PrintHelper from 7.x

**Source**: Microsoft.Toolkit.Uwp.UI.Helpers (7.x)
**Destination**: CommunityToolkit.WinUI.Helpers (8.x) — not yet ported

## Description

The PrintHelper is a Windows Community Toolkit helper class that enables the rendering of a framework element per page for printing purposes.

## Prerequisites

None identified.

## Porting Basics

- [ ] Namespace updated to `CommunityToolkit.WinUI.*`
- [ ] Code for UWP, WinUI3 and Uno Platform consolidated
- [ ] Desired MultiTargets configured
- [ ] Sample code migrated
- [ ] Concept docs migrated
- [ ] Tests migrated and passing

## Quality Evaluation

See [Porting Criteria](https://github.com/CommunityToolkit/Windows/wiki/Component-Quality-Evaluation) for detailed evaluation guidance.

- [n/a] UX: Accessibility reviewed
- [n/a] UX: Visual design reviewed
- [n/a] UX: Interaction patterns appropriate
- [ ] DX: API surface reviewed
- [ ] DX: API flexibility appropriate
- [ ] DX: Documentation updated
- [ ] MX: Breaking changes documented
- [ ] MX: Domain isolation appropriate
- [ ] MX: Test coverage adequate

## Tracking Gaps

*No gaps identified — porting work not yet started.*

## Closing

- [ ] All Porting Basics complete
- [ ] Quality Evaluation reviewed
- [ ] Gaps filed as sub-issues

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## 7x Documentation Inventory

**Docs ported to 8x**: n/a

**Docs not in 8x**: n/a

## 7x Source Inventory

**Source already ported to 8x**: n/a

**Source not ported to 8x**: n/a

## Notes

- Not currently planned for porting. Open to community interest.
- **Archive redirect**: https://learn.microsoft.com/en-us/dotnet/communitytoolkit/windows/archive/printhelper

Beginne mit der archivierten PrintHelper-Referenz und den im Issue verlinkten Porting Criteria; finde die 7.x-Implementierung und bewerte die 8.x-Projektstruktur, bevor du Ziele auswählst. Portiere den Helper nach CommunityToolkit.WinUI.Helpers, migriere Beispiele und Konzeptdokumentation, konfiguriere die angeforderten Ziele und füge bestandene Tests hinzu. Erledigt bedeutet, dass die Checklisten Porting Basics, Quality Evaluation und Closing vollständig abgearbeitet sind.

Vom Indexierungsmodell aus dem Issue-Text verfasst.