build: add Vue and Pinia to the browser build and unit tests

src/testSupport/registerVue.mjs

@@ -0,0 +1,4 @@
+import { register } from 'node:module';
+
+// Lets unit tests import single-file components (`node --import`).
+register('./vueLoader.mjs', import.meta.url);

src/testSupport/vueLoader.mjs

@@ -0,0 +1,39 @@
+import { readFile } from 'node:fs/promises';
+import { fileURLToPath } from 'node:url';
+import { compileScript, compileTemplate, parse } from 'vue/compiler-sfc';
+
+/**
+ * Compile a single-file component to an ES module for Node's test runner.
+ * Styles are dropped: tests read the global stylesheet separately.
+ */
+export function compileVueModule(source, filename) {
+  const { descriptor, errors } = parse(source, { filename });
+  if (errors.length) throw errors[0];
+  const id = filename;
+  if (descriptor.scriptSetup) {
+    return compileScript(descriptor, { id, inlineTemplate: true }).content;
+  }
+  const script = descriptor.script
+    ? compileScript(descriptor, { id }).content.replace(
+        'export default',
+        'const __sfc__ =',
+      )
+    : 'const __sfc__ = {};';
+  const template = descriptor.template
+    ? compileTemplate({ source: descriptor.template.content, filename, id })
+        .code
+    : '';
+  return `${script}\n${template}\n__sfc__.render = typeof render === 'function' ? render : __sfc__.render;\nexport default __sfc__;\n`;
+}
+
+/** Node module hook: load `.vue` files as compiled modules. */
+export async function load(url, context, nextLoad) {
+  if (!url.endsWith('.vue')) return nextLoad(url, context);
+  const filename = fileURLToPath(url);
+  const source = await readFile(filename, 'utf8');
+  return {
+    format: 'module',
+    source: compileVueModule(source, filename),
+    shortCircuit: true,
+  };
+}