Expose exact-target AppInstallManager pause requests

Parent: #232

Dependencies and access restriction

Depends on #233, #234, #236. 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

Manager Pause overloads, with item-level Pause mapping where needed for exact typed identity.

Acceptance criteria

• Resolve exact product/item and scope rather than a display-name match or implicit whole queue.
• Confirm each pause with ShouldProcess, exposing group effects where the API reports them.
• Preserve supported correlation input, native errors and races with completion or item disappearance.
• Report request acceptance separately from observed paused state; do not invent success from a void API.
• Cover already-paused, unsupported-state, grouped-item and preview behavior with deterministic adapters. Preview cannot pause any item.

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.pause
• https://learn.microsoft.com/uwp/api/windows.applicationmodel.store.preview.installcontrol.appinstallitem.pause

Start with parent #232 and dependencies #233, #234, and #236, then read the documented AppInstallManager.Pause and AppInstallItem.Pause references. No implementation file is named; completion requires the compiled-C# contract, supported-access gates, deterministic Pester 6.2+ adapters and coverage, help, documentation, and unreleased notes, while preserving distinct requested and completed outcomes.