Expose explicit free-entitlement acquisition through AppInstallManager

Parent: #232

Dependencies and access restriction

Depends on #233, #234. Implementation remains blocked until the supported-access gate and listed prerequisites are complete.

Microsoft documents AppInstallManager access as protected by a private capability restricted to Microsoft-developed apps. Do not bypass that restriction or treat runFullTrust/admin access alone as sufficient.

API scope

GetFreeDeviceEntitlementAsync, GetFreeUserEntitlementAsync and GetFreeUserEntitlementForUserAsync.

Acceptance criteria

• Treat these Get-prefixed native APIs as state-changing entitlement acquisition, not read-only lookup. Choose an appropriate mutating PowerShell contract.
• Make device-wide, current-user and specified-user scope explicit and mutually exclusive; never silently broaden a user grant to all device users.
• Require ShouldProcess for each product/scope; -WhatIf must not acquire any entitlement.
• Preserve typed entitlement status and native errors. An entitlement grant is not proof of download, installation or a paid purchase.
• No automatic license acquisition by unrelated inventory/search commands, purchase flow, authentication changes or capability bypass.
• Cover supported scope, denied/failed/already-held outcomes, invalid identity, cancellation and preview with deterministic tests only.

Shared delivery requirements

Follow the parent epic's compiled-C# contract, user-scope and capability/version gates. Include deterministic Pester 6.2+ coverage, comment-based help, public documentation and unreleased notes in the same implementation PR. Use fail-closed fake adapters for side effects; no real installs, entitlement grants or settings changes in CI. Preserve original errors and distinguish unavailable, unknown, requested and completed outcomes.

Documented API references

• https://learn.microsoft.com/uwp/api/windows.applicationmodel.store.preview.installcontrol.appinstallmanager.getfreedeviceentitlementasync
• https://learn.microsoft.com/uwp/api/windows.applicationmodel.store.preview.installcontrol.appinstallmanager.getfreeuserentitlementasync
• https://learn.microsoft.com/uwp/api/windows.applicationmodel.store.preview.installcontrol.appinstallmanager.getfreeuserentitlementforuserasync

Start by reading parent issue #232 and dependencies #233 and #234, then review the AppInstallManager entitlement APIs and the parent epic's compiled-C# contract, scope, and capability gates. Use deterministic Pester 6.2+ tests with fail-closed fake adapters; done means all specified scopes and outcomes, ShouldProcess/-WhatIf behavior, help, documentation, and unreleased notes are covered without real side effects.