feat(frontend): support static website demo mode (#3170)

* feat(frontend): support static website demo mode

* fix(frontend): render html artifact previews from blob content

* chore(frontend): apply pre-commit formatting

* fix(frontend): address static demo PR review comments

* Update the release information of DeerFlow

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

frontend/src/core/auth/static-user.ts

@@ -0,0 +1,8 @@
+import type { User } from "./types";
+
+export const STATIC_WEBSITE_USER: User = {
+  id: "static-website-user",
+  email: "static@example.local",
+  system_role: "admin",
+  needs_setup: false,
+};