Add opt-in global brightness shortcuts

[LinkaiQi]

Adds two system-wide keyboard shortcuts that step every connected Apple display's brightness by 10%, without stealing focus from whatever you're doing. Along the way, Settings and About become one window.

Action	Default
Increase brightness by 10%	Win + Ctrl + ↑
Decrease brightness by 10%	Win + Ctrl + ↓

Off by default — nothing is taken over until you turn it on in tray → Settings.

Why these defaults

Win+Ctrl+↑/↓ is one of the few arrow combinations Windows leaves free. Ruled out along the way: Win+↑/↓ (snap), Win+Shift+↑/↓ (stretch across monitors), Win+Alt+↑/↓ (Win11 22H2 half-snap), Ctrl+Alt+arrows (Intel GPU rotation), Ctrl+Shift+arrows (text selection), Win + Plus/Minus (Magnifier). Only Win+Ctrl+←/→ is taken, by virtual desktops.

Both combinations are user-configurable anyway, and a collision is reported rather than swallowed.

How the shortcuts work

• RegisterHotKey binds to the main window's HWND — the same window that already receives WM_DEVICECHANGE, so the shortcuts keep working while the window is hidden in the tray. WM_HOTKEY is dispatched through an HwndSource hook, exactly like the device-change watch.
• MOD_NOREPEAT is set, so one press is one 10% step. Without it a held key auto-repeats ~30×/sec, crossing the whole range in about a third of a second.
• Registration failures surface in the UI. ERROR_HOTKEY_ALREADY_REGISTERED (1409) becomes an inline warning naming the combination; anything else is logged with its Win32 error.
• Recording a shortcut suspends the live ones, otherwise Windows would deliver the combination as WM_HOTKEY and it would never reach the settings window as a key press.
• Settings persist to %LOCALAPPDATA%\NitTray\settings.json, beside the diagnostic log. Load/Save never throw.
• A click-through overlay near the bottom of the primary screen reports the new level, because with the window in the tray there's no other feedback. It never activates and fades out on its own.

One settings window instead of two

Two separate windows for a few hundred pixels of content — each with its own title bar — was clutter. SettingsWindow now hosts a NavigationView rail with Shortcuts in MenuItems and About in FooterMenuItems, mirroring where Windows 11 Settings puts its own About page. AboutWindow is gone; both tray entries and both footer links still work, they just land on different pages of the same window.

About used to be centred while the settings body was a left-aligned form. Putting them one click apart exposed the clash, so About is re-laid-out into the same left-aligned cards.

Notes for reviewers

Two non-obvious framework behaviours drove the design, both verified against source rather than assumed:

• Keyboard.Modifiers never reports the Windows key — KeyboardDevice.cs only computes Alt/Ctrl/Shift. The recorder probes Key.LWin/Key.RWin directly; without that, Win+Ctrl+Up silently records as Ctrl+Up.
• NavigationView constructs pages itself, so each page sets its own DataContext and navigation passes no dataContext — NavigationViewActivator only overwrites DataContext when handed a non-null one.

That second point makes SettingsViewModel a singleton on App, where it used to be rebuilt on every open. Its constructor was the only thing that ever surfaced a registration collision, and CancelCapture blanked the status message unconditionally — so backing out of a recording erased the very warning that prompted it. It now reports the live registration state and refreshes on open.

Known limitation, documented in the UI: Windows doesn't deliver shortcuts to ordinary apps while an elevated window has focus.

⚠️ Not yet tested on Windows. Builds clean (Release + Debug, 0 warnings/errors) and the XAML compiler validates every property name, but no runtime path has been exercised. Worth checking before merge: shortcuts fire while the window is hidden in the tray; the recorder captures Win+Ctrl+↑ intact; a deliberate collision shows the warning; the nav window opens on the right page from each entry point; and the overlay lands correctly on a scaled or multi-monitor setup.