feat: 自定义 OpenAI 兼容上游聚合 + 权重/并发调度

- custom provider:把任意 v1 端点当账号(base_url+key),按 model id 路由,
  直连不走代理;支持 images/generations、images/edits、Sora 式异步视频
- 调度器全局权重优先 + 每账号并发感知(上游账号可配并发,其余系统固定)
- 后台:添加/编辑上游、自定义模型表单(每档普通/代理价,留空=不支持)、
  账号权重/并发列与导入权重
- grok-video / nano-banana-2(runway) 写入硬编码目录(开源自带);
  去掉 540p,Adobe 视频最低 720p
- UI:SelectMenu 与输入框等高、测试耗时改用秒

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

backend/internal/http/router/router.go

@@ -109,6 +109,7 @@ func New(cfg *config.Config, auth *service.AuthService, handlers Handlers) *gin.
 		authed.POST("/tokens/import-krea-cookie", handlers.ProviderAdmin.ImportKreaCookie)
 		authed.POST("/tokens/import-imagine-token", handlers.ProviderAdmin.ImportImagineToken)
 		authed.POST("/tokens/import-grok-token", handlers.ProviderAdmin.ImportGrokToken)
+		authed.POST("/tokens/import-custom-account", handlers.ProviderAdmin.ImportCustomAccount)
 		authed.POST("/tokens/delete-bulk", handlers.ProviderAdmin.TokenDeleteBulk)
 		authed.PATCH("/tokens/:pool/:id", handlers.ProviderAdmin.TokenUpdate)
 		authed.DELETE("/tokens/:pool/:id", handlers.ProviderAdmin.TokenDelete)