[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_windows.go

@@ -0,0 +1,54 @@
+package services
+
+import (
+	"unsafe"
+
+	"github.com/wailsapp/wails/v3/pkg/w32"
+
+	"github.com/netbirdio/netbird/client/ui/preferences"
+)
+
+// setWindowAppearance re-themes a live window's chrome; Wails only does this
+// itself on OS flips for SystemDefault windows.
+//
+// Must run on the UI thread, which Theme.apply guarantees: the uxtheme and
+// repaint calls behind w32.SetTheme belong to the window's thread, and hwnd is
+// only known live while we hold that thread. Re-dispatching here would let the
+// window be destroyed first and hand these writes a reused handle.
+//
+// dark is the appearance Theme.apply already resolved. Re-reading the OS here
+// would let the chrome land on the other side of an OS flip from the window
+// background and the webview.
+func setWindowAppearance(hwnd unsafe.Pointer, _ preferences.Theme, dark bool) {
+	if hwnd == nil || !w32.SupportsThemes() || w32.IsCurrentlyHighContrastMode() {
+		return
+	}
+
+	h := uintptr(hwnd)
+	w32.SetTheme(h, dark)
+
+	// After SetTheme, not before: its menu helper regates dark on the
+	// process-level ShouldAppsUseDarkMode and rewrites the per-window opt-in
+	// with that gated value, so forcing Dark on a light OS would lose it --
+	// and builds below 18985 need the opt-in for the pre-20H1 dark frame. The
+	// gated menu theme name is left alone on purpose: these windows carry no
+	// native menu, and popup-menu text follows the process policy, so forcing
+	// it dark gives dark text on dark.
+	if w32.AllowDarkModeForWindow != nil {
+		w32.AllowDarkModeForWindow(h, dark)
+	}
+
+	chrome := microsoftWindowsLightTheme
+	if dark {
+		chrome = microsoftWindowsDarkTheme
+	}
+	if chrome.TitleBarColour != nil {
+		w32.SetTitleBarColour(h, *chrome.TitleBarColour)
+	}
+	if chrome.TitleTextColour != nil {
+		w32.SetTitleTextColour(h, *chrome.TitleTextColour)
+	}
+	if chrome.BorderColour != nil {
+		w32.SetBorderColour(h, *chrome.BorderColour)
+	}
+}