Fix intermittently reappearing main-window title

[sapsaldog]

Problem

The main window is supposed to show no titlebar title (the glass toolbar is the first content row under a transparent titlebar), but "Oh My Worktree" intermittently appeared next to the traffic lights — sometimes right after opening the window, and it persisted until app restart.

Root cause

A last-writer-wins race between AppKit and SwiftUI on NSWindow.titleVisibility. An lldb breakpoint on -[NSWindow setTitleVisibility:] captured the sequence on the main window:

1. NSHostingView.viewDidMoveToWindow → SwiftUI BarAppearanceBridge.updateWindowTitle sets .visible (bridging ContentView's .navigationTitle("Oh My Worktree"))
2. AppDelegate.configureMainWindowChrome sets .hidden ✓
3. MainWindowChromeConfigurator probe re-applies .hidden ✓
4. Async NSHostingView.preferencesDidChange (ViewGraph render) → BarAppearanceBridge sets .visible again — final writer, title shows

NSHostingController bridges title/toolbar scene preferences to its host window by default, and the bridge re-runs on async preference updates (first layout, content loads, window tiling), so whether the title showed depended on whichever side wrote last. Cold-start window creation (launch → open window ~2s later) reproduced it 3/3.

Fix

Set sceneBridgingOptions = [] on the NSHostingController used for AppDelegate-managed windows, so AppKit stays the sole owner of the window chrome. .navigationTitle stays in ContentView for the WindowGroup path; the manual window's title string is already set via window.title for the title-based window lookup.

Verification

• Cold-start repro protocol (launch → reopen at +2s → screenshot): 3/3 showed the title before the fix, 3/3 clean after
• swiftlint lint clean
• Full test suite: 473 tests in 44 suites pass
• AppDelegate+*.swift is on the coverage exclusion list, so the 100% gate is unaffected

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