fix(web): corrige l'e2e onboarding cassé par l'étape sources

GET /reference/sources n'était intercepté par aucun scénario Cypress
menant à la création/jonction d'un foyer — la requête réelle restait
en attente indéfiniment, laissant OnboardingSourcesPage bloqué sur
/onboarding/sources au lieu de s'auto-sauter vers /onboarding/allergenes.

- Ajout du Given "the sources reference list is empty" (même pattern
  que les intercepts diets/allergies existants), câblé dans les deux
  scénarios qui créent/rejoignent un foyer.
- Mise à jour de l'assertion "Étape 3 sur 3" → "Étape 4 sur 4" : un
  foyer étant créé dans ce scénario, l'étape allergènes affiche
  désormais le total dynamique (4 étapes) comme prévu.
- OnboardingSourcesPage.tsx : redirige aussi vers /onboarding/allergenes
  en cas d'échec réseau sur getSources(), pas seulement quand la liste
  est vide — le wizard ne doit pas bloquer l'utilisateur sur une étape
  optionnelle à cause d'un problème transitoire.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/cypress/e2e/onboarding.feature

@@ -6,11 +6,12 @@ Feature: Onboarding wizard
   Background:
     Given the planning request returns nothing
 
-  Scenario: Walks through all three steps, creating a household on the way, and lands on the home page
+  Scenario: Walks through the wizard, creating a household on the way (which surfaces the sources step), and lands on the home page
     Given the diets reference list has options
     And selecting the diet will succeed
     And the household request returns no household
     And creating a household will succeed
+    And the sources reference list is empty
     And the allergies reference list has options
     And updating allergies will succeed
     And I have signed up
@@ -25,7 +26,7 @@ Feature: Onboarding wizard
     And I click the button "Créer"
     Then the household creation request should have been made with name "Chez Alice"
     And the URL should include "/onboarding/allergenes"
-    And I should see "Étape 3 sur 3"
+    And I should see "Étape 4 sur 4"
     And I should see the section "Allergies"
     And I should see the section "Intolérances"
     When I check the checkbox "Arachides"
@@ -56,6 +57,7 @@ Feature: Onboarding wizard
     And selecting the diet will succeed
     And the household request returns no household
     And joining a household will succeed
+    And the sources reference list is empty
     And the allergies reference list is empty
     And updating allergies will succeed
     And I have signed up

apps/web/cypress/support/step_definitions/reference-data.steps.ts

@@ -31,3 +31,13 @@ Given("the allergies reference list has options", () => {
 Given("the allergies reference list is empty", () => {
   cy.intercept("GET", "**/reference/allergies", { statusCode: 200, body: [] });
 });
+
+// Every onboarding scenario that reaches the household step also reaches
+// `/onboarding/sources` right after (when a household got created/joined —
+// see `OnboardingHouseholdPage`'s `goToNextStep`), which reads this before
+// self-skipping to `/onboarding/allergenes`. No "has options" counterpart
+// yet — no source is implemented in the app itself, so there's nothing
+// real to mock a populated catalog with.
+Given("the sources reference list is empty", () => {
+  cy.intercept("GET", "**/reference/sources", { statusCode: 200, body: [] });
+});

apps/web/src/pages/onboarding/OnboardingSourcesPage.tsx

@@ -44,9 +44,13 @@ export function OnboardingSourcesPage() {
           return;
         }
         setSources(result);
+        setIsLoading(false);
       })
-      .finally(() => {
-        if (!cancelled) setIsLoading(false);
+      .catch(() => {
+        // Nothing to configure sources for if we can't even list them — the
+        // wizard shouldn't strand the visitor here over a transient failure
+        // fetching an optional step's own data.
+        if (!cancelled) navigate("/onboarding/allergenes", { replace: true });
       });
     return () => {
       cancelled = true;