feat: add 'proof of React' challenge (#1038)

* feat: add 'proof of React' challenge

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(challenge/preact): use JSX fragments

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(challenge/preact): ensure that the client waits as long as it needs to

Signed-off-by: Xe Iaso <me@xeiaso.net>

* docs: fix spelling

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(challenges/xeact): add noscript warning

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(challenges/xeact): add default loading message

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(challenges/xeact): make a UI render without JS

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(challenges/xeact): use %s here, not %w

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(test/healthcheck): run asset build

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(challenge/preact): fix build in ci

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>
Signed-off-by: Xe Iaso <xe.iaso@techaro.lol>

lib/challenge/preact/js/xeact.js

@@ -0,0 +1,129 @@
+/**
+ * Creates a DOM element, assigns the properties of `data` to it, and appends all `children`.
+ *
+ * @type{function(string|Function, Object=, Node|Array.<Node|string>=)}
+ */
+const h = (name, data = {}, children = []) => {
+  const result =
+    typeof name == "function" ? name(data) : Object.assign(document.createElement(name), data);
+  if (!Array.isArray(children)) {
+    children = [children];
+  }
+  result.append(...children);
+  return result;
+};
+
+/**
+ * Create a text node.
+ *
+ * Equivalent to `document.createTextNode(text)`
+ *
+ * @type{function(string): Text}
+ */
+const t = (text) => document.createTextNode(text);
+
+/**
+ * Remove all child nodes from a DOM element.
+ *
+ * @type{function(Node)}
+ */
+const x = (elem) => {
+  while (elem.lastChild) {
+    elem.removeChild(elem.lastChild);
+  }
+};
+
+/**
+ * Get all elements with the given ID.
+ *
+ * Equivalent to `document.getElementById(name)`
+ *
+ * @type{function(string): HTMLElement}
+ */
+const g = (name) => document.getElementById(name);
+
+/**
+ * Get all elements with the given class name.
+ *
+ * Equivalent to `document.getElementsByClassName(name)`
+ *
+ * @type{function(string): HTMLCollectionOf.<Element>}
+ */
+const c = (name) => document.getElementsByClassName(name);
+
+/** @type{function(string): HTMLCollectionOf.<Element>} */
+const n = (name) => document.getElementsByName(name);
+
+/**
+ * Get all elements matching the given HTML selector.
+ *
+ * Matches selectors with `document.querySelectorAll(selector)`
+ *
+ * @type{function(string): Array.<HTMLElement>}
+ */
+const s = (selector) => Array.from(document.querySelectorAll(selector));
+
+/**
+ * Generate a relative URL from `url`, appending all key-value pairs from `params` as URL-encoded parameters.
+ *
+ * @type{function(string=, Object=): string}
+ */
+const u = (url = "", params = {}) => {
+  let result = new URL(url, window.location.href);
+  Object.entries(params).forEach((kv) => {
+    let [k, v] = kv;
+    result.searchParams.set(k, v);
+  });
+  return result.toString();
+};
+
+/**
+ * Takes a callback to run when all DOM content is loaded.
+ *
+ * Equivalent to `window.addEventListener('DOMContentLoaded', callback)`
+ *
+ * @type{function(function())}
+ */
+const r = (callback) => window.addEventListener("DOMContentLoaded", callback);
+
+/**
+ * Allows a stateful value to be tracked by consumers.
+ *
+ * This is the Xeact version of the React useState hook.
+ *
+ * @type{function(any): [function(): any, function(any): void]}
+ */
+const useState = (value = undefined) => {
+  return [
+    () => value,
+    (x) => {
+      value = x;
+    },
+  ];
+};
+
+/**
+ * Debounce an action for up to ms milliseconds.
+ *
+ * @type{function(number): function(function(any): void)}
+ */
+const d = (ms) => {
+  let debounceTimer = null;
+  return (f) => {
+    clearTimeout(debounceTimer);
+    debounceTimer = setTimeout(f, ms);
+  };
+};
+
+/**
+ * Parse the contents of a given HTML page element as JSON and
+ * return the results.
+ * 
+ * This is useful when using templ to pass complicated data from
+ * the server to the client via HTML[1].
+ * 
+ * [1]: https://templ.guide/syntax-and-usage/script-templates/#pass-server-side-data-to-the-client-in-a-html-attribute
+ */
+const j = (id) => JSON.parse(g(id).textContent);
+
+export { h, t, x, g, j, c, n, u, s, r, useState, d };