Add polished system feedback overlays

tests/quickshell/osd-ui-contract.sh

@@ -17,6 +17,8 @@ fail() {
 [[ -f "$osd" ]] || fail 'Prism OSD surface is missing'
 [[ -f "$state" ]] || fail 'OSD presentation state is missing'
 [[ -f "$qs_dir/modules/osd/qmldir" ]] || fail 'OSD module manifest is missing'
+rg -q '^import Quickshell$' "$state" \
+    || fail 'OSD singleton does not import the Quickshell Singleton type'
 
 rg -Fq 'import qs.modules.osd' "$shell_file" || fail 'shell does not import the OSD module'
 [[ "$(rg -c '^[[:space:]]*Osd \{\}' "$shell_file")" -eq 1 ]] \