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/serializers.py

@@ -3,7 +3,7 @@ from decimal import Decimal
 from rest_framework import serializers
 
 from apps.accounts.models import Team, TeamMember, User
-from apps.ai.models import AITask, QualityWord
+from apps.ai.models import AITask, ModelConfig, ModelProvider, QualityWord
 from apps.assets.models import Asset
 from apps.billing.models import CreditLedger, QuotaPolicy
 
@@ -133,3 +133,35 @@ class AdminQuotaPolicySerializer(serializers.ModelSerializer):
             "monthly_limit", "project_limit", "per_task_limit", "is_active", "created_at",
         ]
         read_only_fields = ["id", "team_name", "created_at"]
+
+
+class AdminModelProviderSerializer(serializers.ModelSerializer):
+    has_api_key = serializers.SerializerMethodField()
+    model_count = serializers.SerializerMethodField()
+
+    class Meta:
+        model = ModelProvider
+        fields = ["id", "name", "display_name", "status", "base_url", "api_key", "metadata", "has_api_key", "model_count", "created_at"]
+        # api_key 只写不读(密钥不回传前端)
+        extra_kwargs = {"api_key": {"write_only": True, "required": False}}
+        read_only_fields = ["id", "has_api_key", "model_count", "created_at"]
+
+    def get_has_api_key(self, obj) -> bool:
+        return bool(obj.api_key)
+
+    def get_model_count(self, obj) -> int:
+        anno = getattr(obj, "model_count_anno", None)
+        return anno if anno is not None else obj.models.count()
+
+
+class AdminModelConfigSerializer(serializers.ModelSerializer):
+    provider_name = serializers.CharField(source="provider.name", read_only=True, default=None)
+
+    class Meta:
+        model = ModelConfig
+        fields = [
+            "id", "provider", "provider_name", "name", "display_name", "capability",
+            "endpoint", "unit_price", "status", "is_default", "rate_limit_per_minute", "metadata", "created_at",
+        ]
+        # is_default 只经 set-default 端点改,不在普通编辑里直接写
+        read_only_fields = ["id", "provider_name", "is_default", "created_at"]