feat: add system package upgrade to stage 00

- Add PKG_UPGRADE variable to lib/distro.sh:
  - Debian: sudo apt upgrade -y
  - Fedora: sudo dnf upgrade -y
- Export PKG_UPGRADE so stage scripts can use it
- Add upgrade step to 00-envcheck.sh after the existing cache update
  - Errors are non-fatal (|| warn) to handle fresh installs gracefully

lib/distro.sh

@@ -59,6 +59,7 @@ fi
 if [ "$DISTRO_FAMILY" = "debian" ]; then
   PKG_MGR="apt"
   PKG_UPDATE="sudo apt update"
+  PKG_UPGRADE="sudo apt upgrade -y"
   PKG_INSTALL="sudo apt install -y"
   PKG_INSTALL_NO_REC="sudo apt install -y --no-install-recommends"
   PKG_REMOVE="sudo apt remove -y"
@@ -88,6 +89,7 @@ if [ "$DISTRO_FAMILY" = "debian" ]; then
 elif [ "$DISTRO_FAMILY" = "fedora" ]; then
   PKG_MGR="dnf"
   PKG_UPDATE="sudo dnf makecache"
+  PKG_UPGRADE="sudo dnf upgrade -y"
   PKG_INSTALL="sudo dnf install -y"
   PKG_INSTALL_NO_REC="sudo dnf install -y"   # dnf has no --no-install-recommends equivalent
   PKG_REMOVE="sudo dnf remove -y"
@@ -185,7 +187,7 @@ pkg_install_mapped() {
 
 # Export all variables so sourced stages can use them
 export DISTRO_FAMILY DISTRO_ID DISTRO_VERSION DISTRO_CODENAME DISTRO_LIKE
-export PKG_MGR PKG_UPDATE PKG_INSTALL PKG_INSTALL_NO_REC
+export PKG_MGR PKG_UPDATE PKG_UPGRADE PKG_INSTALL PKG_INSTALL_NO_REC
 export PKG_REMOVE PKG_PURGE PKG_AUTOREMOVE
 export PKG_SEARCH PKG_LIST_INSTALLED
 export SERVICE_ENABLE GRUB_UPDATE GRUB_EFI_UPDATE GRUB_FILE

stages/00-envcheck.sh

@@ -36,4 +36,8 @@ fi
 info "Updating package cache (first run)..."
 $PKG_UPDATE 2>/dev/null || warn "Package cache update had issues."
 
+# ---- System upgrade ----
+info "Upgrading all system packages..."
+$PKG_UPGRADE 2>/dev/null || warn "System upgrade had issues (this is okay on a fresh install)."
+
 ok "Stage 00 complete."