Expose guarded AppInstallManager configuration changes

Parent: #232

Dependencies and access restriction

Depends on #233, #234, #238. 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

Supported writes to AcquisitionIdentity and AutoUpdateSetting, subject to the access/context contract. CanInstallForAllUsers is read-only in the C#/WinRT signature and belongs to getter issue #238; do not expose a setter despite the reference summary's misleading "gets or sets" wording.

Acceptance criteria

• Expose only documented writable properties with explicit instance/user/device scope; validate values before any mutation.
• Use the same explicitly identified manager context as related operations. Avoid unnoticed process-global state or settings that are immediately lost in a fresh manager.
• Confirm each property change with ShouldProcess and disclose the target and effect. Preview performs no writes; intrusive update-policy/all-user implications are explicit.
• Do not invent a setter for read-only CanInstallForAllUsers. Its value cannot grant privileges; do not elevate, impersonate another account or claim unavailable capability.
• Preserve setter errors and partial multi-property outcomes; report applied versus not-applied changes without claiming unsupported rollback.
• Where supported, verify observed values after writes. Tests use fake contexts and never change real device/user update policy or acquisition identity.

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.acquisitionidentity
• https://learn.microsoft.com/uwp/api/windows.applicationmodel.store.preview.installcontrol.appinstallmanager.autoupdatesetting
• https://learn.microsoft.com/uwp/api/windows.applicationmodel.store.preview.installcontrol.appinstallmanager.caninstallforallusers

Start with parent issue #232 and dependencies #233, #234, and #238, then review the AppInstallManager properties and compiled-C# contract described here. Use fake contexts and fail-closed adapters for deterministic Pester 6.2+ tests; done means supported writable properties validate and report changes without real device or user-policy effects, while preserving errors and partial outcomes.