Add the web interface

Plain HTML, CSS and JavaScript modules, with no build step. Hash routes
and relative URLs make it work under any path. The job list is polled:
every 2 seconds while a job runs, and less often otherwise.

tests/js/proxy-reload.test.mjs

@@ -0,0 +1,31 @@
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+import { find, install, server, settle } from './flow-helpers.mjs';
+
+const ui = install();
+const { api, setUnauthorizedHandler } = await import('../../bindery/static/js/lib.js');
+const { stopPolling } = await import('../../bindery/static/js/jobs.js');
+
+// The proxy login page has no form to retry from, and a fetch keeps the proxy's own session
+// cookie, so only a full page load lets the proxy step in again.
+test('a 401 while logged in through the proxy reloads the page', async (t) => {
+  t.after(() => {
+    stopPolling();
+    setUnauthorizedHandler(() => {});
+  });
+  const backend = server(t);
+  backend.on('GET', 'auth/check', { authenticated: true, mode: 'proxy', user: 'alice' });
+  backend.on('GET', 'config', { metadata_fields: {}, mode_labels: {}, library_available: false });
+  backend.on('GET', 'jobs', []);
+  backend.on('GET', 'stories', []);
+  backend.on('GET', 'expired', { error: 'Session ended' }, 401);
+  await import('../../bindery/static/js/main.js');
+  await settle();
+  assert.match(ui.app.textContent, /alice/);
+  let reloaded = 0;
+  window.location.reload = () => reloaded++;
+  await assert.rejects(api('expired'), /Session ended/);
+  await settle();
+  assert.equal(reloaded, 1);
+  assert.equal(backend.sent('GET', 'auth/check').length, 1);
+});