feat: implement security, discovery, history, file transfer, web UI (P0-P3)

internal/notify/notify.go

@@ -0,0 +1,11 @@
+// Package notify provides best-effort desktop notifications.
+//
+// Each platform file defines its own implementation using //go:build tags:
+// Linux uses notify-send, macOS uses osascript, Windows is a no-op (Windows
+// toast notifications require a registered app or a third-party module).
+package notify
+
+// Notifier sends a desktop notification.
+type Notifier interface {
+	Notify(title, body string) error
+}