Rewrite variety score and suggestions with configurable scoring

- Add VarietyScoreConfig entity, repository, and V020 migration for
  per-household scoring weights and configurable tag types
- Rewrite getVarietyScore: tag-type repeats on consecutive days,
  non-staple ingredient overlaps, cooking log history, plan duplicates
- Rewrite getSuggestions: simulate variety score for each candidate,
  add tag filter (AND, case-insensitive) and configurable topN param
- Update SuggestionResponse to return simulatedScore instead of
  fitReasons/warnings, update VarietyScoreResponse to new shape
- Seed default VarietyScoreConfig on household creation
- Extend test suite across all domains (+270 tests, all passing)

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

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

@@ -9,6 +9,7 @@ import com.recipeapp.household.dto.*;
 import com.recipeapp.household.entity.Household;
 import com.recipeapp.household.entity.HouseholdInvite;
 import com.recipeapp.household.entity.HouseholdMember;
+import com.recipeapp.planning.VarietyScoreConfigRepository;
 import com.recipeapp.recipe.IngredientCategoryRepository;
 import com.recipeapp.recipe.IngredientRepository;
 import com.recipeapp.recipe.TagRepository;
@@ -36,6 +37,7 @@ class HouseholdServiceTest {
     @Mock private IngredientRepository ingredientRepository;
     @Mock private IngredientCategoryRepository ingredientCategoryRepository;
     @Mock private TagRepository tagRepository;
+    @Mock private VarietyScoreConfigRepository varietyScoreConfigRepository;
 
     @InjectMocks
     private HouseholdServiceImpl householdService;
@@ -191,4 +193,67 @@ class HouseholdServiceTest {
         assertThatThrownBy(() -> householdService.acceptInvite("tom@example.com", "USED123"))
                 .isInstanceOf(ConflictException.class);
     }
+
+    @Test
+    void acceptInviteShouldThrowWhenInviteNotFound() {
+        var user = new UserAccount("tom@example.com", "Tom", "hashed");
+
+        when(userAccountRepository.findByEmailIgnoreCase("tom@example.com")).thenReturn(Optional.of(user));
+        when(householdMemberRepository.findByUserEmailIgnoreCase("tom@example.com")).thenReturn(Optional.empty());
+        when(householdInviteRepository.findByInviteCode("INVALID")).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> householdService.acceptInvite("tom@example.com", "INVALID"))
+                .isInstanceOf(ResourceNotFoundException.class);
+    }
+
+    @Test
+    void acceptInviteShouldThrowWhenUserNotFound() {
+        when(userAccountRepository.findByEmailIgnoreCase("unknown@example.com")).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> householdService.acceptInvite("unknown@example.com", "ABC12XYZ"))
+                .isInstanceOf(ResourceNotFoundException.class);
+    }
+
+    @Test
+    void createHouseholdShouldThrowWhenUserNotFound() {
+        when(userAccountRepository.findByEmailIgnoreCase("unknown@example.com")).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> householdService.createHousehold(
+                "unknown@example.com", new CreateHouseholdRequest("New")))
+                .isInstanceOf(ResourceNotFoundException.class);
+    }
+
+    @Test
+    void getMembersShouldReturnAllMembers() {
+        var user1 = testUser();
+        var user2 = new UserAccount("tom@example.com", "Tom", "hashed");
+        var household = new Household("Smith family", user1);
+        var member1 = new HouseholdMember(household, user1, "planner");
+        var member2 = new HouseholdMember(household, user2, "member");
+
+        when(householdMemberRepository.findByUserEmailIgnoreCase("sarah@example.com")).thenReturn(Optional.of(member1));
+        when(householdMemberRepository.findByHouseholdId(any())).thenReturn(List.of(member1, member2));
+
+        List<MemberResponse> result = householdService.getMembers("sarah@example.com");
+
+        assertThat(result).hasSize(2);
+        assertThat(result.get(0).displayName()).isEqualTo("Sarah");
+        assertThat(result.get(1).displayName()).isEqualTo("Tom");
+    }
+
+    @Test
+    void getMembersShouldThrowWhenUserNotInHousehold() {
+        when(householdMemberRepository.findByUserEmailIgnoreCase("orphan@example.com")).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> householdService.getMembers("orphan@example.com"))
+                .isInstanceOf(ResourceNotFoundException.class);
+    }
+
+    @Test
+    void createInviteShouldThrowWhenUserNotInHousehold() {
+        when(householdMemberRepository.findByUserEmailIgnoreCase("orphan@example.com")).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> householdService.createInvite("orphan@example.com"))
+                .isInstanceOf(ResourceNotFoundException.class);
+    }
 }