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>

nginx.conf

@@ -16,12 +16,21 @@ server {
         return 200 "ok\n";
     }
 
-    # Vendor libs can be cached hard.
+    # Vendor libs + fonts can be cached hard.
     location /vendor/ {
         expires 30d;
         add_header Cache-Control "public, immutable";
     }
 
+    # Service worker and manifest must always revalidate.
+    location = /sw.js {
+        add_header Cache-Control "no-cache";
+    }
+    location = /manifest.webmanifest {
+        default_type application/manifest+json;
+        add_header Cache-Control "no-cache";
+    }
+
     # Never cache the app shell, so updates land immediately.
     location = /index.html {
         add_header Cache-Control "no-cache";