scripts: make Build-Pack and Deploy-Brass cross-platform

Two small fixes that surface when running the deploy pipeline on a
non-Windows host (we now do this on glados via the Telegram bridge):

- Build-Pack.ps1: fall back to launcher/ModpackLauncher.csproj <Version>
  when Get-Item.VersionInfo.FileVersion returns empty. Linux PowerShell
  can't parse PE FileVersion from a Windows .exe, so the previous code
  threw "set <Version> in ModpackLauncher.csproj and republish" -- but
  the csproj <Version> *was* set, just not readable from a foreign PE.
  Appends ".0" so the embedded value still matches the 4-part form the
  Windows compile bakes in.

- Deploy-Brass.ps1: prefer rsync where available, fall back to robocopy
  otherwise. robocopy is Windows-only and bails on Linux/macOS hosts.

scripts/Build-Pack.ps1

@@ -163,8 +163,25 @@ if ($LauncherExePath) {
     }
     $launcherFile = Get-Item $LauncherExePath
     $launcherVersion = $launcherFile.VersionInfo.FileVersion
+    $versionSource   = 'PE FileVersion'
+
+    # Linux PowerShell can't read PE FileVersion from a Windows .exe. When that
+    # happens, fall back to launcher/ModpackLauncher.csproj's <Version> (the
+    # source of truth that the Windows compile bakes into FileVersion anyway).
+    # Append ".0" so callers get the same 4-part form as the PE metadata.
     if ([string]::IsNullOrWhiteSpace($launcherVersion)) {
-        throw "Launcher exe has no FileVersion -- set <Version> in ModpackLauncher.csproj and republish."
+        $csprojPath = Join-Path $here '..\launcher\ModpackLauncher.csproj'
+        if (Test-Path $csprojPath) {
+            [xml]$csproj = Get-Content $csprojPath
+            $csprojVersion = ($csproj.Project.PropertyGroup.Version | Where-Object { $_ }) | Select-Object -First 1
+            if ($csprojVersion) {
+                $launcherVersion = if ($csprojVersion -match '^\d+\.\d+\.\d+$') { "$csprojVersion.0" } else { $csprojVersion }
+                $versionSource = "csproj <Version> (fallback)"
+            }
+        }
+    }
+    if ([string]::IsNullOrWhiteSpace($launcherVersion)) {
+        throw "Launcher exe has no FileVersion and csproj <Version> couldn't be read either -- set <Version> in ModpackLauncher.csproj and republish."
     }
     # FileVersion is the four-component form (e.g. "0.1.0.0" for csproj <Version>0.1.0</Version>).
     # Embed as-is -- the launcher's Version.Parse handles it directly and avoids ambiguous
@@ -174,7 +191,7 @@ if ($LauncherExePath) {
 
     Write-Host ""
     Write-Host ("Launcher metadata embedded:")
-    Write-Host ("  Version:  {0}" -f $launcherVersion)
+    Write-Host ("  Version:  {0}  ({1})" -f $launcherVersion, $versionSource)
     Write-Host ("  Url:      {0}" -f $LauncherPublicUrl)
     Write-Host ("  Source:   {0}" -f $launcherFile.FullName)
 }