feat(auth): add @RequiresHouseholdRole annotation with interceptor

Reusable annotation for planner-only endpoints. Uses a
HandlerInterceptor that resolves the household role from the
authenticated user and throws 403 if the role doesn't match.

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

backend/src/main/java/com/recipeapp/common/WebMvcConfig.java

@@ -0,0 +1,20 @@
+package com.recipeapp.common;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
+import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
+
+@Configuration
+public class WebMvcConfig implements WebMvcConfigurer {
+
+    private final HouseholdRoleInterceptor householdRoleInterceptor;
+
+    public WebMvcConfig(HouseholdRoleInterceptor householdRoleInterceptor) {
+        this.householdRoleInterceptor = householdRoleInterceptor;
+    }
+
+    @Override
+    public void addInterceptors(InterceptorRegistry registry) {
+        registry.addInterceptor(householdRoleInterceptor);
+    }
+}