feat: 新增Snippet全局内容模型（TeamMember/Testimonial/Partner/NavigationMenu/SiteSettings）

- 新增 apps.core.TeamMember/Testimonial/Partner：简单 register_snippet，含 order 排序字段
- 新增 apps.core.NavigationMenu+NavigationMenuItem：ClusterableModel+Orderable+InlinePanel，
  支持内部页面或外部链接二选一
- 新增 apps.core.SiteSettings：接入 wagtail.contrib.settings + BaseSiteSetting，
  存放公司信息/ICP备案号/社交账号等全局配置
- 新增只读 API：/api/v1/custom/core/{team,testimonials,partners,navigation,site-settings}/
- 补充 apps/core/tests.py 单元测试，pytest 用例由 11 个增至 24 个，全部通过
- 更新设计文档 §2.16 Phase 1 进度清单

apps/core/api.py

@@ -0,0 +1,67 @@
+"""
+apps.core 全局 Snippet 只读接口。挂载在 /api/v1/custom/core/
+（详见 apps/core/urls.py 与 documents/设计方案分析与完善版.md §2.7）。
+公开只读数据，限流走 DRF ScopedRateThrottle 的 "public" scope（100/min）。
+"""
+from rest_framework.response import Response
+from rest_framework.throttling import ScopedRateThrottle
+from rest_framework.views import APIView
+
+from .models import NavigationMenu, Partner, SiteSettings, TeamMember, Testimonial
+from .serializers import (
+    NavigationMenuSerializer,
+    PartnerSerializer,
+    SiteSettingsSerializer,
+    TeamMemberSerializer,
+    TestimonialSerializer,
+)
+
+
+class TeamMemberListView(APIView):
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "public"
+
+    def get(self, request, *args, **kwargs):
+        members = TeamMember.objects.all()
+        return Response({"items": TeamMemberSerializer(members, many=True).data})
+
+
+class TestimonialListView(APIView):
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "public"
+
+    def get(self, request, *args, **kwargs):
+        testimonials = Testimonial.objects.all()
+        return Response({"items": TestimonialSerializer(testimonials, many=True).data})
+
+
+class PartnerListView(APIView):
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "public"
+
+    def get(self, request, *args, **kwargs):
+        partners = Partner.objects.all()
+        return Response({"items": PartnerSerializer(partners, many=True).data})
+
+
+class NavigationMenuView(APIView):
+    """根据 ?name= 查询指定导航菜单（如 main / footer）。"""
+
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "public"
+
+    def get(self, request, *args, **kwargs):
+        name = request.query_params.get("name", "main")
+        menu = NavigationMenu.objects.prefetch_related("items").filter(name=name).first()
+        if menu is None:
+            return Response({"error": {"code": "NOT_FOUND", "message": "导航菜单不存在"}}, status=404)
+        return Response(NavigationMenuSerializer(menu).data)
+
+
+class SiteSettingsView(APIView):
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "public"
+
+    def get(self, request, *args, **kwargs):
+        settings_obj = SiteSettings.for_request(request)
+        return Response(SiteSettingsSerializer(settings_obj).data)