Fix contextual dismissal with live portal mirroring

[muukii]

Contextual dismissal snapshots can show a capture-protection placeholder instead of the visible content. Use a live portal for the outgoing view and let the portal hide its source while preserving the existing mask, transforms, and cross-fade timing.

Hiding the source layer leaves its view in hit testing. Disable interaction on the outgoing view and temporary mirror container so touches can reach the destination list during dismissal. Restore the source's previous interaction setting on completion, cancellation, or interruption.

Validation:

• FluidStackControllerTests: 21 tests passed on iPhone 18 Pro / iOS 27.0 using FluidInterfaceKit-Package.
• Swift syntax check and git diff --check passed.
• GitHub CI stops before compilation: the existing workflow selects Xcode 26.0 / Swift 6.2, while Package.swift on main requires Swift tools 6.3. See the failed build.
• Normal close and edge dismissal were checked in the host app with the initial portal change. The final interaction adjustment has not been independently rechecked during an active animation in the host app; that rebuild stopped on a shared build database lock. The existing tests do not cover this gesture behavior.