fix(welcome): wire WindowOpener bridge from all scenes to fix missing-window race

[datlechin]

Summary

Welcome window sometimes failed to appear on launch and Dock-icon clicks did nothing. Console showed:
```
WindowOpener call queued; bridge not yet wired
WindowOpener call queued; bridge not yet wired
WindowOpener call queued; bridge not yet wired
```
…and the queue never drained.

Root cause

`WindowOpenerBridge` is the SwiftUI view that hands `openWindow` / `openSettings` closures to the AppKit-world `WindowOpener` singleton. It was mounted only in the Welcome scene and wired itself in `.onAppear { wireUp() }`.

If state restoration or a launch intent caused Welcome to be `orderOut`'d before its view body's first appearance, `.onAppear` never fired, the bridge never wired, and every subsequent `WindowOpener.shared.openWelcome()` call from `AppLaunchCoordinator` / `applicationShouldHandleReopen` / etc. was queued indefinitely. The app would launch with no visible window and Dock-icon clicks would silently queue more calls onto the dead queue.

Fix

1. Mount `WindowOpenerBridge` in all four SwiftUI scenes: Welcome, ConnectionForm, IntegrationsActivity, Settings. Whichever scene materializes first triggers the wire-up; subsequent scenes call `wire(...)` again, which is idempotent (overwrites the same closures, drains the now-empty queue).
2. Switch `.onAppear` → `.task`. `.task` fires reliably when the view enters the hierarchy, even if it never reaches the visible state.

Test plan

• Launch the app cleanly (no restored state). Welcome window appears.
• Launch with a restored connection window. Welcome window does NOT appear (correct), but clicking the Dock icon shows Welcome.
• Cmd+, to open Settings works.
• Click "+" to open New Connection works.
• Console has no "WindowOpener call queued; bridge not yet wired" warnings during normal launch.