feat: Implement the ChatGPT Owner Demotion Console with new frontend and backend components.

backend/internal/api/demote.go

@@ -0,0 +1,36 @@
+package api
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"codex-pool/internal/demote"
+)
+
+// HandleDemoteOwner POST /api/demote/owner - Owner 降级
+func HandleDemoteOwner(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		Error(w, http.StatusMethodNotAllowed, "仅支持 POST")
+		return
+	}
+
+	var req demote.DemoteRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		Error(w, http.StatusBadRequest, "无效的请求: "+err.Error())
+		return
+	}
+
+	if req.AccessToken == "" {
+		Error(w, http.StatusBadRequest, "access_token 不能为空")
+		return
+	}
+
+	// 默认角色
+	if req.Role == "" {
+		req.Role = "standard-user"
+	}
+
+	result := demote.DemoteOwner(req)
+
+	Success(w, result)
+}