SwiftUI: confirm thread deletion from the thread list #6106

Problem

In the native SwiftUI thread list, both the swipe action and row menu call deleteThread immediately. A stray destructive action permanently removes the thread without a confirmation step.

This is particularly risky beside reversible lifecycle actions such as Settle, Archive, Snooze, and Unpin.

Proposed behavior

• Route every thread-list Delete entry point through one confirmation alert.
• Name the thread in the alert when its title is available.
• Keep Cancel as the default action and Delete as a destructive action.
• Perform the existing deletion only after explicit confirmation.
• Do not change archive, settle, snooze, pin, or server deletion semantics.

Scope

The existing owner is apps/swift-ios/Features/Workspace/WorkspaceView.swift; no protocol or server change is required.

Acceptance

• Swipe/menu Delete opens a confirmation instead of deleting immediately.
• Cancel leaves the thread untouched.
• Confirm invokes deletion for the intended thread exactly once.
• The alert remains usable with large Dynamic Type.