feat(admin): Phase 8 模型供应商管理 — provider/model CRUD + 启停 + 定价 + 设默认

后端:ModelConfig.is_default + migration;get_default_model 优先 is_default 否则回落最早 active(零回归);
adminpanel providers CRUD(api_key write-only 不回传)+ models CRUD(?provider/capability 筛)+ set-default(同 capability 清旧);
IsPlatformAdmin + 审计。
前端:adminApi providers/models/setDefault;Admin 模型供应商页(供应商表+模型表+启停+定价+设默认+供应商/模型弹窗)。
测试:adminpanel 51 单测过(api_key 隐藏+入库/CRUD/set-default 改 get_default_model);
apps.ai 仍仅 3 个进场前既有失败(零回归);无头 e2e _admin-p8.mjs 5 断言过 + 0 console error
(用一次性禁用 provider+model capability=export,无副作用,跑完删);tsc+build 绿。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

core/backend/apps/adminpanel/urls.py

@@ -7,6 +7,11 @@ from .views import (
     admin_invitations,
     admin_ledger_adjust,
     admin_ledgers,
+    admin_model_detail,
+    admin_model_set_default,
+    admin_models,
+    admin_provider_detail,
+    admin_providers,
     admin_quota_policies,
     admin_quota_policy_detail,
     admin_task_detail,
@@ -45,4 +50,9 @@ urlpatterns = [
     path("ledgers/adjust/", admin_ledger_adjust, name="admin-ledger-adjust"),
     path("quota-policies/", admin_quota_policies, name="admin-quota-policies"),
     path("quota-policies/<uuid:policy_id>/", admin_quota_policy_detail, name="admin-quota-policy-detail"),
+    path("providers/", admin_providers, name="admin-providers"),
+    path("providers/<uuid:provider_id>/", admin_provider_detail, name="admin-provider-detail"),
+    path("models/", admin_models, name="admin-models"),
+    path("models/<uuid:model_id>/", admin_model_detail, name="admin-model-detail"),
+    path("models/<uuid:model_id>/set-default/", admin_model_set_default, name="admin-model-set-default"),
 ]