Wrap the top bar's buttons onto a second row when narrow (closes #272)

The top bar's two sides were held apart only by justify-between, with
no gap and no wrapping, so at 390 px "by @sneak" ended where the New
App button began. The bar's row now wraps and has a gap: in a window
too narrow for one row, New App and Logout move to a second row; on
wider windows the bar looks as before.

Model: opus-5-5

internal/handlers/dashboard_layout_test.go

@@ -52,3 +52,26 @@ func TestDashboardTableFitsCard(t *testing.T) {
 	assert.Contains(t, cellTag, "whitespace-normal")
 	assert.Contains(t, cellTag, "break-all")
 }
+
+// TestTopBarWrapsWhenNarrow checks that the top bar keeps a gap between the
+// µPaaS title and the New App and Logout buttons, and puts the buttons on a
+// second row in a window too narrow for one, instead of letting them meet.
+func TestTopBarWrapsWhenNarrow(t *testing.T) {
+	t.Parallel()
+
+	testCtx := setupTestHandlers(t)
+
+	request := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
+	recorder := httptest.NewRecorder()
+
+	testCtx.handlers.HandleDashboard().ServeHTTP(recorder, request)
+
+	require.Equal(t, http.StatusOK, recorder.Code)
+
+	_, afterNav, found := strings.Cut(recorder.Body.String(), `<nav class="app-bar">`)
+	require.True(t, found, "dashboard has no top bar")
+
+	rowTag, _, _ := strings.Cut(strings.TrimSpace(afterNav), ">")
+	assert.Contains(t, rowTag, "flex-wrap")
+	assert.Contains(t, rowTag, "gap-")
+}