docs: add reference Python/Flask implementation

Previous version of Tanabata used as visual and functional reference
for the new Go + SvelteKit rewrite.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/reference/web/static/js/auth.js

@@ -0,0 +1,19 @@
+$("#auth").on("submit", function submit(e) {
+	e.preventDefault();
+	$.ajax({
+		url: "/auth",
+		type: "POST",
+		data: $("#auth").serialize(),
+		dataType: "json",
+		success: function(resp) {
+			if (resp.status) {
+				location.reload();
+			} else {
+				alert(resp.error);
+			}
+		},
+		failure: function(err) {
+			alert(err);
+		}
+	});
+});