Implement SyncWarden v0.1.0

Full Syncthing tray wrapper with:
- System tray with 5 icon states (idle/syncing/paused/error/disconnected)
- Syncthing REST API client with auto-discovered API key
- Long-polling event listener for real-time status
- Transfer rate monitoring, folder tracking, recent files, conflict counting
- Full context menu with folders, recent files, settings toggles
- Embedded admin panel binary (webview, requires CGO)
- OS notifications via beeep (per-event configurable)
- Syncthing process management with auto-restart
- Cross-platform installer with autostart
- CI pipeline for Linux (.deb + .tar.gz) and Windows (.zip)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/setup/ui_windows.go

@@ -0,0 +1,28 @@
+//go:build windows
+
+package main
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+var (
+	user32      = syscall.NewLazyDLL("user32.dll")
+	messageBoxW = user32.NewProc("MessageBoxW")
+)
+
+func showMessage(title, text string, isError bool) {
+	flags := uint32(0x00000040) // MB_ICONINFORMATION
+	if isError {
+		flags = 0x00000010 // MB_ICONERROR
+	}
+
+	titlePtr, _ := syscall.UTF16PtrFromString(title)
+	textPtr, _ := syscall.UTF16PtrFromString(text)
+	messageBoxW.Call(0,
+		uintptr(unsafe.Pointer(textPtr)),
+		uintptr(unsafe.Pointer(titlePtr)),
+		uintptr(flags),
+	)
+}