Add Vitest tests for the languages, router, footer and pages, and a lint:check script

vitest.config.js

@@ -0,0 +1,25 @@
+import { defineConfig } from 'vite'
+import { fileURLToPath, URL } from 'node:url'
+import vue from '@vitejs/plugin-vue'
+
+// Tailwind's plugin is left out on purpose: the tests check what a page says
+// and links to, not how it looks.
+export default defineConfig({
+  plugins: [vue()],
+  resolve: {
+    alias: {
+      '@': fileURLToPath(new URL('./src', import.meta.url)),
+    },
+  },
+  test: {
+    environment: 'jsdom',
+    environmentOptions: {
+      jsdom: { url: 'http://localhost:5173' },
+    },
+    globals: true,
+    setupFiles: ['./tests/setup.js'],
+    // The first test to mount a big view pays for compiling it too.
+    testTimeout: 20000,
+    hookTimeout: 20000,
+  },
+})