feat(Sora): 直连生成并移除sora2api依赖

实现直连 Sora 客户端、媒体落地与清理策略\n更新网关与前端配置以支持 Sora 平台\n补齐单元测试与契约测试，新增 curl 测试脚本\n\n测试: go test ./... -tags=unit

frontend/src/views/admin/GroupsView.vue

@@ -1363,11 +1363,6 @@ const createForm = reactive({
   sora_image_price_540: null as number | null,
   sora_video_price_per_request: null as number | null,
   sora_video_price_per_request_hd: null as number | null,
-  // Sora 按次计费配置
-  sora_image_price_360: null as number | null,
-  sora_image_price_540: null as number | null,
-  sora_video_price_per_request: null as number | null,
-  sora_video_price_per_request_hd: null as number | null,
   // Claude Code 客户端限制（仅 anthropic 平台使用）
   claude_code_only: false,
   fallback_group_id: null as number | null,