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>

frontend/src/components/SelectMenu.vue

@@ -73,7 +73,7 @@ onUnmounted(() => document.removeEventListener('mousedown', onDocClick))
     <button type="button" @click="toggle" @keydown="onKeydown"
             :aria-expanded="open"
             :disabled="disabled"
-            class="field flex items-center justify-between gap-2 text-left disabled:opacity-50 disabled:cursor-not-allowed"
+            class="field flex items-center justify-between gap-2 text-left h-10 !py-0 disabled:opacity-50 disabled:cursor-not-allowed"
             :class="[mono ? 'font-mono' : '', selected ? '' : 'text-[color:var(--fg-faint)]']">
       <span class="truncate">{{ label }}</span>
       <Icon name="chevron"