feat: improve daemon resilience, streaming, and usenet downloads

- Add daemon state persistence and stale resume file cleanup
- Add TriggerPoll for WebSocket resume actions
- Improve stream server with graceful shutdown and connection tracking
- Add desktop notifications for download completion
- Add media file organization with Movies/TV Shows detection
- Improve usenet downloader with progress tracking and resume support
- Add self-update package with GitHub release verification
- Downgrade tablewriter to v0.0.5 (v1.x API breaking change)

internal/engine/notify.go

@@ -14,8 +14,29 @@ func desktopNotify(title, body string) {
 	case "darwin":
 		script := `display notification "` + escapeAppleScript(body) + `" with title "` + escapeAppleScript(title) + `"`
 		exec.Command("osascript", "-e", script).Start()
+	case "windows":
+		// Use PowerShell toast notification (Windows 10+)
+		script := `[Windows.UI.Notifications.ToastNotificationManager, Windows.UI.Notifications, ContentType = WindowsRuntime] > $null;` +
+			`$xml = [Windows.UI.Notifications.ToastNotificationManager]::GetTemplateContent(1);` +
+			`$text = $xml.GetElementsByTagName('text');` +
+			`$text[0].AppendChild($xml.CreateTextNode('` + escapePowerShell(title) + `')) > $null;` +
+			`$text[1].AppendChild($xml.CreateTextNode('` + escapePowerShell(body) + `')) > $null;` +
+			`$toast = [Windows.UI.Notifications.ToastNotification]::new($xml);` +
+			`[Windows.UI.Notifications.ToastNotificationManager]::CreateToastNotifier('unarr').Show($toast)`
+		exec.Command("powershell", "-NoProfile", "-Command", script).Start()
 	}
-	// Windows: no-op for now
+}
+
+func escapePowerShell(s string) string {
+	out := make([]byte, 0, len(s))
+	for i := 0; i < len(s); i++ {
+		if s[i] == '\'' {
+			out = append(out, '\'', '\'') // double single-quote to escape
+		} else {
+			out = append(out, s[i])
+		}
+	}
+	return string(out)
 }
 
 func escapeAppleScript(s string) string {