feat(members): implement DELETE/PATCH member + GET invites backend endpoints

- Add V006 migration: invalidated_at column + partial unique index on household_invite
- Add findByHouseholdIdAndInvalidatedAtIsNull, findByHouseholdIdAndUserId, countByHouseholdIdAndRole
- Add ChangeRoleRequest DTO
- HouseholdService: getActiveInvite, createInvite (regenerate), removeMember, changeMemberRole
- HouseholdController: GET /v1/households/mine/invites, DELETE/PATCH /v1/households/mine/members/{userId}

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

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

@@ -9,6 +9,8 @@ import org.springframework.web.bind.annotation.*;
 
 import java.security.Principal;
 import java.util.List;
+import java.util.Optional;
+import java.util.UUID;
 
 @RestController
 @RequestMapping("/v1")
@@ -40,12 +42,35 @@ public class HouseholdController {
         return ResponseEntity.ok(members);
     }
 
+    @GetMapping("/households/mine/invites")
+    public ResponseEntity<ApiResponse<InviteResponse>> getActiveInvite(Principal principal) {
+        Optional<InviteResponse> invite = householdService.getActiveInvite(principal.getName());
+        return invite
+                .map(r -> ResponseEntity.ok(ApiResponse.success(r)))
+                .orElse(ResponseEntity.noContent().build());
+    }
+
     @PostMapping("/households/mine/invites")
     public ResponseEntity<ApiResponse<InviteResponse>> createInvite(Principal principal) {
         InviteResponse response = householdService.createInvite(principal.getName());
         return ResponseEntity.status(HttpStatus.CREATED).body(ApiResponse.success(response));
     }
 
+    @DeleteMapping("/households/mine/members/{userId}")
+    public ResponseEntity<Void> removeMember(Principal principal, @PathVariable UUID userId) {
+        householdService.removeMember(principal.getName(), userId);
+        return ResponseEntity.noContent().build();
+    }
+
+    @PatchMapping("/households/mine/members/{userId}")
+    public ResponseEntity<ApiResponse<MemberResponse>> changeMemberRole(
+            Principal principal,
+            @PathVariable UUID userId,
+            @Valid @RequestBody ChangeRoleRequest request) {
+        MemberResponse response = householdService.changeMemberRole(principal.getName(), userId, request.role());
+        return ResponseEntity.ok(ApiResponse.success(response));
+    }
+
     @PostMapping("/invites/{code}/accept")
     public ResponseEntity<ApiResponse<AcceptInviteResponse>> acceptInvite(
             Principal principal,