[client] Add light mode with system, light, and dark theme options (#7344)

* desktop UI light mode

* Theme review fixes plus macOS window outline fix

* Windows runtime chrome re-theming plus apply serialization

* Windows chrome threading and theme event ordering fixes

* Darken toggle and setting sidebar text

* resolve theme appearance, apply on UI thread

* read theme once per window

* Re-assert Windows dark opt-in after SetTheme

* split app-wide GTK theming from per-window chrome

* Update Wails dependency and checksums

* KDE tray icon panel fix

* Five review fixes: theme ordering, cgo dedup, KDE panel resolution

* Path guard hardening, toggle contrast, windows comment

* non-vacuous escape tests

* Default view edits

* Polish settings nav, controls, borders, and disc

* Profiles settings boarder, modals, and buttons

* Additional edits based on feedback

* Switch colors away from slight blue hue

* Update missing lang

* Fix vertical tab active view

client/ui/services/windowappearance_darwin.go

@@ -0,0 +1,53 @@
+package services
+
+/*
+#cgo CFLAGS: -x objective-c
+#cgo LDFLAGS: -framework AppKit
+
+#import <AppKit/AppKit.h>
+
+// forced < 0: follow the OS (appearance nil); 0: light; 1: dark.
+//
+// Assigns directly rather than dispatching: Theme.apply already runs this on
+// the main thread. Deferring would outlive the caller's check that the window
+// is alive, and the __bridge cast does not retain it, so the block could touch
+// a freed NSWindow.
+static void nbSetWindowAppearance(void *nsWindow, int forced) {
+	NSWindow *window = (__bridge NSWindow *)nsWindow;
+	if (forced < 0) {
+		window.appearance = nil;
+	} else {
+		NSAppearanceName name = forced == 1 ? NSAppearanceNameDarkAqua : NSAppearanceNameAqua;
+		window.appearance = [NSAppearance appearanceNamed:name];
+	}
+}
+*/
+import "C"
+
+import (
+	"unsafe"
+
+	"github.com/netbirdio/netbird/client/ui/preferences"
+)
+
+// setWindowAppearance pins the NSWindow appearance to the forced theme, or
+// hands it back to the OS for ThemeSystem. Without this, a window created
+// under one OS appearance keeps its dark/light frame after a manual theme
+// flip, leaving a mismatched border around the webview. Must run on the main
+// thread, which Theme.apply guarantees.
+//
+// The resolved appearance is unused: for ThemeSystem a nil NSAppearance lets
+// AppKit track the OS itself, which cannot drift from a snapshot we took.
+func setWindowAppearance(nsWindow unsafe.Pointer, pref preferences.Theme, _ bool) {
+	if nsWindow == nil {
+		return
+	}
+	forced := C.int(-1)
+	switch pref {
+	case preferences.ThemeLight:
+		forced = 0
+	case preferences.ThemeDark:
+		forced = 1
+	}
+	C.nbSetWindowAppearance(nsWindow, forced)
+}