feat(ui): render application templates as Vue views mounted before wiring

Templates listed in build/applicationViews.js expand to mount hosts, and
mountApplicationViews() renders them before translation and wiring. Markup
tests read the page through a server-side render helper, the i18n scanner
reads view templates, and Vue preserves whitespace so views keep the exact
DOM. No template is converted yet.

src/testSupport/applicationHtml.mjs

@@ -0,0 +1,40 @@
+import { readFileSync } from 'node:fs';
+import { createPinia } from 'pinia';
+import { createSSRApp } from 'vue';
+import { renderToString } from 'vue/server-renderer';
+import { expandApplicationHtml } from '../../build/application-html.js';
+import { APPLICATION_VIEWS } from '../ui/views/index.js';
+
+const HOST = /<div class="gev-view" data-gev-view="([^"]+)"><\/div>/g;
+
+/**
+ * Expand application markup as the browser shows it once views are mounted:
+ * static templates inline, and each view rendered into its host. Markup tests
+ * read this instead of the raw template expansion.
+ * @param {string} html Document with `gev:template` markers.
+ * @returns {Promise<string>}
+ */
+export async function renderApplicationHtml(html) {
+  let output = expandApplicationHtml(html);
+  for (const [host, name] of [...output.matchAll(HOST)]) {
+    const view = APPLICATION_VIEWS[name];
+    if (!view) throw new Error(`Unknown application view: ${name}`);
+    const markup = (await renderToString(createSSRApp(view).use(createPinia())))
+      // Hydration markers and empty-attribute values are SSR detail; the
+      // DOM is the same as the template's.
+      .replace(/<!--\[-->|<!--\]-->|<!---->/g, '')
+      .replace(/ ([\w:.-]+)=""/g, ' $1');
+    output = output.replace(
+      host,
+      `<div class="gev-view" data-gev-view="${name}">${markup}</div>`,
+    );
+  }
+  return output;
+}
+
+/** The standalone page's markup with every view rendered. */
+export function readApplicationHtml() {
+  return renderApplicationHtml(
+    readFileSync(new URL('../../index.html', import.meta.url), 'utf8'),
+  );
+}