refactor(schematics): derive the empty-features warning from the prompt message

The empty-features warning duplicated the checkbox prompt's message as a
second string literal, so a reworded prompt would leave the warning
pointing at text the user never sees. Export the message as a shared
constant and reference it in both places, matching the shared-constant
pattern used for the firebase-tools version message in 59c8a2f.

Author: armando-navarro

src/schematics/setup/index.ts

@@ -16,7 +16,7 @@ import {
   parseDataConnectConfig,
   setupTanstackDependencies,
 } from '../utils';
-import { appPrompt, featuresPrompt, projectPrompt, userPrompt } from './prompts';
+import { appPrompt, featuresPrompt, featuresPromptMessage, projectPrompt, userPrompt } from './prompts';
 
 // FirebaseOptions keys — apps.sdkconfig responses include management-API extras that initializeApp() rejects.
 const firebaseOptionsKeys = [
@@ -65,7 +65,7 @@ export const ngAddSetupProject = (
   if (features.length === 0) {
     context.logger.warn(
       'No features were selected, so there is nothing to set up. ' +
-      'At the "What features would you like to setup?" prompt, use the arrow keys to move, ' +
+      `At the "${featuresPromptMessage}" prompt, use the arrow keys to move, ` +
       'press Space to select each feature you want, then Enter to confirm. ' +
       'Re-run ng add @angular/fire to try again.'
     );

src/schematics/setup/prompts.ts

@@ -79,12 +79,14 @@ type Prompt = <K extends string, U= unknown>(questions: { name: K, source: (...a
 const autocomplete: Prompt = (questions) => inquirer.prompt(questions);
 
 
+export const featuresPromptMessage = 'What features would you like to setup?';
+
 export const featuresPrompt = async (): Promise<FEATURES[]> => {
   const { features } = await inquirer.prompt({
     type: 'checkbox',
     name: 'features',
     choices: featureOptions,
-    message: 'What features would you like to setup?',
+    message: featuresPromptMessage,
     default: [],
   }) as { features: FEATURES[] };
   return features;