feat: add reading stats and replace dashboard charts with recharts

Add currently reading, recently read, and reading activity sections to
the dashboard. Replace all custom SVG/CSS charts with recharts library
(donut, area, stacked bar, horizontal bar). Reorganize layout: libraries
and popular series side by side, books added chart full width below.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/backoffice/package.json

@@ -12,6 +12,7 @@
     "next-themes": "^0.4.6",
     "react": "19.0.0",
     "react-dom": "19.0.0",
+    "recharts": "^3.8.0",
     "sanitize-html": "^2.17.1"
   },
   "devDependencies": {