Say env var changes take effect at the next deploy or rollback (closes #255)

The hint under the app page's environment variable editor asked for a
container restart. Environment variables are set when a container is
created, and upaas's restart stops and starts the same container, so it
keeps the old values; deploy and rollback each create a new container.
The hint now says so in one sentence, styled with alert-warning like the
page's Volume Mounts note: its old text-amber-600 class is not in the
built stylesheet. A handler test renders the app page and checks the
hint.

Model: opus-5-5

internal/handlers/app_page_env_var_hint_test.go

@@ -0,0 +1,39 @@
+package handlers_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"sneak.berlin/go/upaas/internal/service/app"
+)
+
+// TestAppPageEnvVarHint checks that the environment variable editor says
+// changes take effect at the next deploy or rollback, in the warning style.
+func TestAppPageEnvVarHint(t *testing.T) {
+	t.Parallel()
+
+	testCtx := setupTestHandlers(t)
+
+	createdApp, err := testCtx.appSvc.CreateApp(t.Context(), app.CreateAppInput{
+		Name:    "env-hint-app",
+		RepoURL: "git@example.com:user/env-hint-app.git",
+	})
+	require.NoError(t, err)
+
+	request := httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/apps/"+createdApp.ID, nil,
+	)
+	request = addChiURLParams(request, map[string]string{"id": createdApp.ID})
+	recorder := httptest.NewRecorder()
+
+	testCtx.handlers.HandleAppDetail().ServeHTTP(recorder, request)
+
+	require.Equal(t, http.StatusOK, recorder.Code)
+	assert.Contains(t, recorder.Body.String(),
+		`<p class="alert-warning mt-1">`+
+			"Environment variable changes take effect at the next deploy or rollback.</p>")
+}