Fail the package audit when the manifest is missing

Reading a nonexistent manifest produced an empty package list, so the audit
reported every package installed after checking none of them.

test/acceptance.d/system-test.sh

@@ -8,12 +8,17 @@ status=0
 
 verify_core_packages() {
   local package
+  local manifest="$OMARCHY_PATH/install/omarchy-base.packages"
   local -a missing=()
 
+  # Without this, a missing manifest reads as an empty package list and the
+  # audit passes having checked nothing.
+  [[ -f $manifest ]] || fail "all Omarchy core packages are installed" "package manifest not found: $manifest"
+
   while IFS= read -r package; do
     [[ -z $package || $package == \#* ]] && continue
     pacman -Q "$package" >/dev/null 2>&1 || missing+=("$package")
-  done <"$OMARCHY_PATH/install/omarchy-base.packages"
+  done <"$manifest"
 
   (( ${#missing[@]} == 0 )) || fail "all Omarchy core packages are installed" "missing packages: ${missing[*]}"
   pass "all Omarchy core packages are installed (${#missing[@]} missing)"