feat(group-filter): 分组账号过滤控制 — require_oauth_only + require_privacy_set

为 OpenAI/Antigravity/Anthropic/Gemini 分组新增两个布尔控制字段：
- require_oauth_only: 创建/更新账号绑定分组时拒绝 apikey 类型加入
- require_privacy_set: 调度选号时跳过 privacy 未成功设置的账号并标记 error

后端：Ent schema 新增字段 + 迁移、Group CRUD 全链路透传、
      gateway_service 与 openai_account_scheduler 两套调度路径过滤
前端：创建/编辑表单 toggle 开关（OpenAI/Antigravity/Anthropic/Gemini 平台可见）

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/ent/migrate/schema.go

@@ -409,6 +409,8 @@ var (
 		{Name: "supported_model_scopes", Type: field.TypeJSON, SchemaType: map[string]string{"postgres": "jsonb"}},
 		{Name: "sort_order", Type: field.TypeInt, Default: 0},
 		{Name: "allow_messages_dispatch", Type: field.TypeBool, Default: false},
+		{Name: "require_oauth_only", Type: field.TypeBool, Default: false},
+		{Name: "require_privacy_set", Type: field.TypeBool, Default: false},
 		{Name: "default_mapped_model", Type: field.TypeString, Size: 100, Default: ""},
 	}
 	// GroupsTable holds the schema information for the "groups" table.