feat(backend): make invite share URL base configurable via app.base-url

Replaces hardcoded \"https://yourapp.com\" with a Spring property.

- application.yml: app.base-url defaults to http://localhost:5173
- application-docker.yml: reads APP_BASE_URL env var, same default
- HouseholdService: injects @Value("${app.base-url}") and uses it in
  toInviteResponse() to build shareUrl
- HouseholdServiceTest: sets field via ReflectionTestUtils in @BeforeEach;
  adds test asserting shareUrl starts with configured base URL

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/com/recipeapp/household/HouseholdService.java

@@ -17,6 +17,7 @@ import com.recipeapp.recipe.TagRepository;
 import com.recipeapp.recipe.entity.Ingredient;
 import com.recipeapp.recipe.entity.IngredientCategory;
 import com.recipeapp.recipe.entity.Tag;
+import org.springframework.beans.factory.annotation.Value;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
@@ -38,6 +39,9 @@ public class HouseholdService {
     private final TagRepository tagRepository;
     private final VarietyScoreConfigRepository varietyScoreConfigRepository;
 
+    @Value("${app.base-url}")
+    private String baseUrl;
+
     private static final SecureRandom RANDOM = new SecureRandom();
     private static final String CODE_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 
@@ -262,7 +266,7 @@ public class HouseholdService {
     private InviteResponse toInviteResponse(HouseholdInvite invite) {
         return new InviteResponse(
                 invite.getInviteCode(),
-                "https://yourapp.com/join/" + invite.getInviteCode(),
+                baseUrl + "/join/" + invite.getInviteCode(),
                 invite.getExpiresAt());
     }
 }

backend/src/main/resources/application-docker.yml

@@ -2,3 +2,6 @@ spring:
   flyway:
     locations: classpath:db/migration,classpath:db/seed
     out-of-order: true
+
+app:
+  base-url: ${APP_BASE_URL:http://localhost:5173}

backend/src/main/resources/application.yml

@@ -30,3 +30,6 @@ spring:
 
 server:
   port: 8080
+
+app:
+  base-url: http://localhost:5173

backend/src/test/java/com/recipeapp/household/HouseholdServiceTest.java

@@ -17,7 +17,9 @@ import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.InjectMocks;
 import org.mockito.Mock;
+import org.junit.jupiter.api.BeforeEach;
 import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.test.util.ReflectionTestUtils;
 
 import java.time.Instant;
 import java.util.List;
@@ -43,6 +45,11 @@ class HouseholdServiceTest {
     @InjectMocks
     private HouseholdService householdService;
 
+    @BeforeEach
+    void setUp() {
+        ReflectionTestUtils.setField(householdService, "baseUrl", "http://localhost:5173");
+    }
+
     private UserAccount testUser() {
         return new UserAccount("sarah@example.com", "Sarah", "hashed");
     }
@@ -132,6 +139,21 @@ class HouseholdServiceTest {
         verify(householdInviteRepository).save(any(HouseholdInvite.class));
     }
 
+    @Test
+    void createInviteShouldBuildShareUrlWithConfiguredBaseUrl() {
+        var user = testUser();
+        var household = new Household("Smith family", user);
+        var member = new HouseholdMember(household, user, "planner");
+
+        when(householdMemberRepository.findByUserEmailIgnoreCase("sarah@example.com")).thenReturn(Optional.of(member));
+        when(householdInviteRepository.save(any(HouseholdInvite.class))).thenAnswer(i -> i.getArgument(0));
+
+        InviteResponse result = householdService.createInvite("sarah@example.com");
+
+        assertThat(result.shareUrl()).startsWith("http://localhost:5173/join/");
+        assertThat(result.shareUrl()).endsWith(result.inviteCode());
+    }
+
     @Test
     void acceptInviteShouldAddUserAsMember() {
         var user = new UserAccount("tom@example.com", "Tom", "hashed");