feat: add selected update installs and polished UI

internal/gui/server_test.go

@@ -0,0 +1,11 @@
+package gui
+
+import "testing"
+
+func TestShellPackageList(t *testing.T) {
+	got := shellPackageList([]string{"vapoursynth", "libastal-4-git", "vapoursynth", "bad package"})
+	want := "'vapoursynth' 'libastal-4-git'"
+	if got != want {
+		t.Fatalf("shellPackageList() = %q, want %q", got, want)
+	}
+}