Add desktop shortcuts, document the real Prism export zip format

install.ps1/install.sh now create a desktop shortcut/.desktop entry
that launches straight into the game, so participants don't have to
re-run the install script or hunt through folders after closing the
launcher once.

Also root-caused the "no instance in Fjord" report: Prism's Export
Instance zips the instance contents (instance.cfg, mmc-pack.json,
minecraft/) directly at the zip root, NOT wrapped in a folder named
after the instance like HOSTING.md assumed. Fixed by repackaging the
live modpack.zip server-side with the correct LANParty/ wrapper
(verified real exported files - actual Java path, real playtime
stats, not fabricated). HOSTING.md still needs a correction pass to
stop telling people to expect a pre-wrapped export.

install.ps1

@@ -85,5 +85,16 @@ if (-not (Test-Path (Join-Path "instances" $InstanceName))) {
     Write-Host "==> Instance already present, skipping download"
 }
 
+# Desktop shortcut so the game is findable after closing it, without re-running this script
+$ShortcutPath = Join-Path ([Environment]::GetFolderPath("Desktop")) "LAN Party Minecraft.lnk"
+$WshShell = New-Object -ComObject WScript.Shell
+$Shortcut = $WshShell.CreateShortcut($ShortcutPath)
+$Shortcut.TargetPath = $LauncherBin
+$Shortcut.Arguments = "--dir `"$InstallDir`" --launch $InstanceName --profile `"$Nick`" --server $ServerAddr"
+$Shortcut.WorkingDirectory = Split-Path $LauncherBin
+$Shortcut.IconLocation = $LauncherBin
+$Shortcut.Save()
+Write-Host "==> Desktop shortcut created: $ShortcutPath (double-click this next time instead of re-running the install script)"
+
 Write-Host "==> Launching into $InstanceName as $Nick, joining $ServerAddr"
 & $LauncherBin --dir $InstallDir --launch $InstanceName --profile $Nick --server $ServerAddr