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

remote-install.sh

@@ -9,7 +9,8 @@
 #
 set -eu
 
-ARCHIVE_URL="https://git.mosaicstack.dev/mosaic/bootstrap/archive/main.tar.gz"
+BOOTSTRAP_REF="${MOSAIC_BOOTSTRAP_REF:-main}"
+ARCHIVE_URL="https://git.mosaicstack.dev/mosaic/bootstrap/archive/${BOOTSTRAP_REF}.tar.gz"
 TMPDIR_BASE="${TMPDIR:-/tmp}"
 WORK_DIR="$TMPDIR_BASE/mosaic-bootstrap-$$"
 
@@ -18,7 +19,7 @@ cleanup() {
 }
 trap cleanup EXIT
 
-echo "[mosaic] Downloading bootstrap archive..."
+echo "[mosaic] Downloading bootstrap archive (ref: $BOOTSTRAP_REF)..."
 
 mkdir -p "$WORK_DIR"