[Samples]: Define how migrated samples land in WindowsAppSDK-Samples

@niels9001 is already working on this.

Since Aug 5, 2026.

## Is your feature request related to a problem? Please describe.

The migrated samples need a supported home in `microsoft/WindowsAppSDK-Samples`, but that repository currently uses more than one organizational pattern. Some APIs are grouped into consolidated feature applications such as `Samples/Input/cs-winui`, while other proposed migrations use standalone feature folders.

Scaling submissions before maintainers agree on the structure could produce duplicated shells, inconsistent naming, oversized applications, fragmented CI, and pull requests that cannot land cleanly on `main`.

## Describe the solution you'd like

Define and validate a maintainers-approved repository structure and landing process for the migrated WinUI 3 samples.

The decision should cover:

- Criteria for standalone samples versus scenarios consolidated into an existing feature application.
- Feature-area taxonomy, folder names, language/configuration suffixes, project names, and scenario naming.
- Alignment with the repository's WinUI sample templates and sample-authoring guidelines.
- Shared shell, assets, package identity, manifests, versioning, and Windows App SDK package conventions.
- Per-feature README files, repository README registration, and Docs Samples Browser metadata.
- CI pipeline ownership, `SamplesCI-All.yml` registration, build matrices, launch testing, accessibility, WACK, and internal Aggregator onboarding.
- Code ownership and the expected size/batching of migration pull requests.
- How samples flow from `niels9001/winui-samples` into reviewed pull requests targeting `main`.

Use a representative pilot to prove the chosen structure, then document the rule so the remaining sample ports can follow it consistently.

### Completion criteria

- Windows App SDK sample maintainers approve the organizational and contribution model.
- Standalone-versus-consolidated criteria are documented with examples.
- Required repository, metadata, CI, ownership, and validation changes are enumerated.
- At least one representative migrated sample follows the agreed model and lands on `main`.
- The remaining migration backlog can be partitioned into reviewable pull requests without reopening the structural decision.

## Additional context

Relevant precedents:

- `microsoft/WindowsAppSDK-Samples#649` proposes standalone `FocusVisuals` and `TouchKeyboard` feature folders.
- `microsoft/WindowsAppSDK-Samples#650` adds migrated scenarios to the consolidated `Samples/Input/cs-winui` application.
- The viable-port and blocker inventories are tracked in the two companion issues created for this effort.