Fix #82 : Submission form remains open after successful feature submission

[byaruhaf]

Problem

On macOS, after successfully submitting a new wish via CreateWishView, the success alert was never appearing. Users would tap Save and nothing visible would happen no confirmation, no window close even though the wish was successfully created on the backend.

Root cause

CreateWishView had two separate .alert(isPresented:) modifiers attached to the same view one driven by alertModel.showAlert and another by showConfirmationAlert. On macOS, two separate .alert(isPresented:) modifiers on the same view appear to conflict the success alert's content was built but never actually presented on screen.

Fix

• Replaced both .alert(isPresented:) modifiers with a single .alert(item:) driven by one ActiveAlert enum, so there's exactly one alert presentation attached to the view at any time.
• Moved createActionCompletion() / closeAction() directly into the alert's own dismissButton action, so they only fire once SwiftUI has taken ownership of dismissing that alert — removing the need for the DispatchQueue.main.async workaround.
• Added a synchronous guard (guard !viewModel.isButtonLoading) at the top of submitAction() to prevent double-submission from rapid double clicks.
• Removed the now-unused AlertModel and presentationMode dependency.

Testing

• Verified single Save tap → success alert appears → tapping OK closes the sheet and refreshes the list.
• Verified Cancel with unsaved text still shows the discard confirmation alert and behaves correctly.