Expose wallpaper health status

tests/quickshell/health-service-contract.sh

@@ -47,6 +47,8 @@ fail() {
 [[ -f "$service" ]] || fail 'Health.qml is missing'
 [[ -f "$source_harness" ]] || fail 'health harness is missing'
 [[ -f "$shell" ]] || fail 'shell.qml is missing'
+rg -q 'target: "wallpaper"' "$shell" \
+    || fail 'wallpaper health target is not exported by the shell'
 
 # shell.qml is not started here: it is the active desktop shell. Keep this
 # contract static while pinning the typed, redacted IPC boundary it exports.