Add JS tests, refactor SitemapController, extract JS modules

- Extract mobile-menu.js and tabs.js from app.js
- Add Vitest tests with happy-dom and v8 coverage (100% on modules)
- Add JS test step to CI frontend and SonarQube workflows
- SonarQube: add JS lcov coverage report path
- SitemapController: extract URLSET_TEMPLATE constant, deduplicate methods

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vitest.config.js

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+    test: {
+        environment: 'happy-dom',
+        include: ['tests/js/**/*.test.js'],
+        coverage: {
+            provider: 'v8',
+            include: ['assets/modules/**/*.js'],
+            reporter: ['text', 'lcov'],
+        },
+    },
+})