v2: light editorial redesign, bilingual (EN-first), preview, front matter, PWA

Design (design-taste-frontend + ui-ux-design-pro + impeccable):
- Warm, flat, light editorial theme (OKLCH), Geist + Geist Mono, single vermilion accent
- Dark mode toggle, persisted; respects prefers-color-scheme
- Prominent focus rings, tactile states, reduced-motion

Features (GitHub-ready):
- i18n EN/DE, English default, persisted
- Live split preview (marked + DOMPurify, sanitized)
- Optional YAML front matter (title/date/source/tags), rendered as metadata block
- Conversion options: links as text, strip images, bullet marker, heading style
- Filename patterns (title+date / date+time), auto/custom indicator
- Drag & drop .html/.md/.txt, reading time
- Installable PWA + service worker (offline), README (EN) + MIT LICENSE

Fix: switch inputs were covered by decorative spans (pointer-events).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sw.js

@@ -0,0 +1,43 @@
+/* clip2md service worker — offline shell cache. Bump CACHE on any asset change. */
+var CACHE = 'clip2md-v2';
+var ASSETS = [
+  './',
+  './index.html',
+  './icon.svg',
+  './manifest.webmanifest',
+  './vendor/turndown.js',
+  './vendor/turndown-plugin-gfm.js',
+  './vendor/marked.umd.js',
+  './vendor/purify.min.js',
+  './vendor/fonts/Geist-Variable.woff2',
+  './vendor/fonts/GeistMono-Variable.woff2'
+];
+
+self.addEventListener('install', function (e) {
+  self.skipWaiting();
+  e.waitUntil(caches.open(CACHE).then(function (c) { return c.addAll(ASSETS); }));
+});
+
+self.addEventListener('activate', function (e) {
+  e.waitUntil(
+    caches.keys().then(function (keys) {
+      return Promise.all(keys.filter(function (k) { return k !== CACHE; }).map(function (k) { return caches.delete(k); }));
+    }).then(function () { return self.clients.claim(); })
+  );
+});
+
+self.addEventListener('fetch', function (e) {
+  if (e.request.method !== 'GET') return;
+  e.respondWith(
+    caches.match(e.request).then(function (hit) {
+      return hit || fetch(e.request).then(function (res) {
+        // Runtime-cache same-origin successful responses.
+        if (res && res.ok && e.request.url.indexOf(self.location.origin) === 0) {
+          var copy = res.clone();
+          caches.open(CACHE).then(function (c) { c.put(e.request, copy); });
+        }
+        return res;
+      }).catch(function () { return caches.match('./index.html'); });
+    })
+  );
+});