fix: detect Batocera and Knulli by build files

No Batocera build writes /etc/batocera-version: batocera-system.mk:21-22
(batocera.linux 38845725, unchanged since batocera-30) writes
/usr/share/batocera/batocera.version. Knulli (knulli-linux 57afa662) adds
OS_NAME=knulli to os-release, writes /usr/share/knulli/knulli.version and
removes /usr/share/batocera, and no Knulli source writes /etc/knulli-release.
Neither was detected. A Knulli board is named and not narrowed by
Batocera's per-board lists, and an unlisted board is named.

install.ps1

@@ -11,7 +11,7 @@
 
     $ErrorActionPreference = "Stop"
     $defaultInstallUrl = "https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-    $defaultInstallSha256 = "e85a34efb84620b8c65858d209c9741a715f8ff6a61397f9ee161c0931a9a049"
+    $defaultInstallSha256 = "5ed37d4dabc5a6b28a9093f38a25506b20ec2f49c3587692efd695b017d1caf4"
     $maximumInstallerBytes = 2MB
     $installerExit = 0
     $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }