fix(greeter): restore legacy remembered sessions by desktop id

- Derive a desktop id from legacy remembered session paths
- Match remembered sessions by desktop id before falling back to path

core/internal/qmlchecks/greeter_session_memory_test.go

@@ -0,0 +1,22 @@
+package qmlchecks
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestGreeterRememberLastSessionFallsBackToDesktopID(t *testing.T) {
+	data, err := os.ReadFile("../../../quickshell/Modules/Greetd/GreeterContent.qml")
+	if err != nil {
+		t.Fatalf("read greeter QML: %v", err)
+	}
+
+	content := string(data)
+	if !strings.Contains(content, "GreetdMemory.lastSessionDesktopId || desktopIdFromPath(GreetdMemory.lastSessionId)") {
+		t.Fatalf("remembered greeter sessions should derive a desktop id from legacy absolute session paths")
+	}
+	if !strings.Contains(content, "GreeterState.sessionDesktopIds[i] === savedDesktopId") {
+		t.Fatalf("remembered greeter sessions should match current sessions by desktop id")
+	}
+}