Add startup application picker

tests/quickshell/applications-settings-contract.sh

@@ -33,6 +33,9 @@ done
 assert_contains 'title: "Default applications"'
 assert_contains 'title: "User autostart"'
 assert_contains 'title: "Compositor autostart"'
+assert_contains 'AutostartAppPicker {'
+assert_contains 'DefaultApps.addAutostart('
+assert_contains 'label: "Add an application"'
 assert_contains 'categories'
 assert_contains 'genericName'
 assert_contains '.sort('
@@ -123,4 +126,14 @@ fi
 [[ "$(rg --count 'activatable:' "$page")" -ge 2 ]] \
     || fail 'default and autostart rows are not both whole-row activatable'
 
+picker="$project_root/config/dot/quickshell/modules/settings/AutostartAppPicker.qml"
+qmldir="$project_root/config/dot/quickshell/modules/settings/qmldir"
+[[ -f "$picker" ]] || fail 'autostart application picker is missing'
+rg -Fq 'required property var existing' "$picker" \
+    || fail 'autostart picker cannot exclude existing entries'
+rg -Fq 'signal picked(string id)' "$picker" \
+    || fail 'autostart picker does not emit a validated desktop id'
+rg -q '^AutostartAppPicker 1\.0 AutostartAppPicker\.qml$' "$qmldir" \
+    || fail 'autostart picker is not registered in the Settings module'
+
 printf 'applications settings contract: PASS\n'