fix(ui): restore brand across anonymous and error pages

Assisted-by: Codex:GPT-5

services/context/context_response.go

@@ -166,6 +166,7 @@ func (ctx *Context) notFoundInternal(logMsg string, logErr error) {
 	ctx.Data["IsRepo"] = ctx.Repo.Repository != nil
 	ctx.Data["Title"] = "Page Not Found"
 	ctx.Data["ErrorMsg"] = "" // FIXME: the template never renders this message, need to fix in the future (and show safe messages to end users)
+	ctx.Data["ShowNavbarBrand"] = true
 	ctx.HTML(http.StatusNotFound, "status/404")
 }