Update scripts to keep SOUL.md idempotent. Add release upgrade framework.

remote-install.ps1

@@ -8,12 +8,13 @@
 #
 $ErrorActionPreference = "Stop"
 
-$ArchiveUrl = "https://git.mosaicstack.dev/mosaic/bootstrap/archive/main.zip"
+$BootstrapRef = if ($env:MOSAIC_BOOTSTRAP_REF) { $env:MOSAIC_BOOTSTRAP_REF } else { "main" }
+$ArchiveUrl = "https://git.mosaicstack.dev/mosaic/bootstrap/archive/$BootstrapRef.zip"
 $WorkDir = Join-Path $env:TEMP "mosaic-bootstrap-$PID"
 $ZipPath = "$WorkDir.zip"
 
 try {
-    Write-Host "[mosaic] Downloading bootstrap archive..."
+    Write-Host "[mosaic] Downloading bootstrap archive (ref: $BootstrapRef)..."
     New-Item -ItemType Directory -Path $WorkDir -Force | Out-Null
     Invoke-WebRequest -Uri $ArchiveUrl -OutFile $ZipPath -UseBasicParsing