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.

.gitignore

@@ -0,0 +1,22 @@
+# Dependencies
+node_modules/
+
+# Logs
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Editor files
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# The dist/ directory contains generated minified assets.
+# It is intentionally committed so the theme works without running npm install.
+# If you prefer to generate it in CI, uncomment the next line.
+# dist/