fix: define missing --font-md and --success-soft-bg tokens

Both were referenced by components (RecommendationShelf, the manga detail
page) but never declared, so var() fell through to inherited/fallback
values. Adds --font-md (1rem, on the xs/sm/md/lg scale) and
--success-soft-bg in both the light and dark theme blocks.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.114.0",
+  "version": "0.114.1",
   "private": true,
   "type": "module",
   "scripts": {