Add asset pipeline and professionalize theme

Introduce a Node build system for minified CSS/JS with content hashes,
add PWA support, i18n helpers, accessibility improvements, and more
translatable strings. Move theme configuration from bookmarks to
localStorage, add Playwright tests, and set up CI workflows.

shaarli-pro/playwright.config.js

@@ -0,0 +1,33 @@
+/**
+ * Playwright configuration for Shaarli Pro theme smoke tests.
+ *
+ * These tests assume a running Shaarli instance with the shaarli-pro theme
+ * activated. Set the SHAARLI_URL environment variable to point to it.
+ *
+ * Example:
+ *   SHAARLI_URL=http://localhost:8080 npx playwright test
+ */
+'use strict';
+
+const { defineConfig, devices } = require('@playwright/test');
+
+const baseURL = process.env.SHAARLI_URL || 'http://localhost:8080';
+
+module.exports = defineConfig({
+    testDir: './tests',
+    fullyParallel: true,
+    forbidOnly: !!process.env.CI,
+    retries: process.env.CI ? 2 : 0,
+    workers: process.env.CI ? 1 : undefined,
+    reporter: 'list',
+    use: {
+        baseURL,
+        trace: 'on-first-retry',
+        screenshot: 'only-on-failure'
+    },
+    projects: [
+        { name: 'chromium', use: { ...devices['Desktop Chrome'] } },
+        { name: 'firefox', use: { ...devices['Desktop Firefox'] } },
+        { name: 'webkit', use: { ...devices['Desktop Safari'] } }
+    ]
+});