PrimaryLanguageOverride always return null/empty

Nobody has claimed this yet.

### Describe the bug

`Microsoft.Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride` is not persisted across app relaunch (unlike UWP behavior).

`ApplicationLanguages.PrimaryLanguageOverride` behaves differently in WinUI 3 compared to UWP (Windows.Globalization).

In UWP, once PrimaryLanguageOverride is set and the app is **relaunched**, the value is persisted and can be read again.
In WinUI 3, after relaunching the application, **PrimaryLanguageOverride** always returns **null** or an **empty string**, even though it was previously set successfully.

This creates a behavior inconsistency between UWP and WinUI and makes it impossible to rely on `PrimaryLanguageOverride` for persistent language selection.

Is this behavior by design, or is it a bug / missing implementation in Microsoft.Windows.Globalization?

If by design, documentation should explicitly state that PrimaryLanguageOverride is not persisted in WinUI 3.

Sorry guys for tagging you:
@stefansjfw
@kmahone
@riverar

### Steps to reproduce the bug

1.Create a WinUI 3 desktop application.
2.Set the language override:
`Microsoft.Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride = "en-US";`
3.Close the application.
4.Relaunch the application.
5.Read:

`Debug.WriteLine(Microsoft.Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride);`

### Expected behavior

After relaunch, PrimaryLanguageOverride should still return the previously set value (same behavior as UWP Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride).

### Screenshots

_No response_

### NuGet package version
Latest
None

### Packaging type
Packaged
_No response_

### Windows version
11 Latest
_No response_

### IDE
VS2026
_No response_

### Additional context

_No response_

Start by investigating Microsoft.Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride in the WinUI 3 desktop path and compare its relaunch behavior with UWP Windows.Globalization. Reproduce the packaged-app steps, then determine whether the intended outcome is persistence or explicit documentation that the value is not persisted.

Written by the indexing model from the issue text.