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/lib/api.ts

@@ -550,9 +550,32 @@ export type MetadataStats = {
   by_provider: ProviderCount[];
 };
 
+export type CurrentlyReadingItem = {
+  book_id: string;
+  title: string;
+  series: string | null;
+  current_page: number;
+  page_count: number;
+};
+
+export type RecentlyReadItem = {
+  book_id: string;
+  title: string;
+  series: string | null;
+  last_read_at: string;
+};
+
+export type MonthlyReading = {
+  month: string;
+  books_read: number;
+};
+
 export type StatsResponse = {
   overview: StatsOverview;
   reading_status: ReadingStatusStats;
+  currently_reading: CurrentlyReadingItem[];
+  recently_read: RecentlyReadItem[];
+  reading_over_time: MonthlyReading[];
   by_format: FormatCount[];
   by_language: LanguageCount[];
   by_library: LibraryStatsItem[];

apps/backoffice/lib/i18n/en.ts

@@ -82,6 +82,12 @@ const en: Record<TranslationKey, string> = {
   "dashboard.bookMetadata": "Book metadata",
   "dashboard.withSummary": "With summary",
   "dashboard.withIsbn": "With ISBN",
+  "dashboard.currentlyReading": "Currently reading",
+  "dashboard.recentlyRead": "Recently read",
+  "dashboard.readingActivity": "Reading activity (last 12 months)",
+  "dashboard.pageProgress": "p. {{current}} / {{total}}",
+  "dashboard.noCurrentlyReading": "No books in progress",
+  "dashboard.noRecentlyRead": "No books read recently",
 
   // Books page
   "books.title": "Books",

apps/backoffice/lib/i18n/fr.ts

@@ -80,6 +80,12 @@ const fr = {
   "dashboard.bookMetadata": "Métadonnées livres",
   "dashboard.withSummary": "Avec résumé",
   "dashboard.withIsbn": "Avec ISBN",
+  "dashboard.currentlyReading": "En cours de lecture",
+  "dashboard.recentlyRead": "Derniers livres lus",
+  "dashboard.readingActivity": "Activité de lecture (12 derniers mois)",
+  "dashboard.pageProgress": "p. {{current}} / {{total}}",
+  "dashboard.noCurrentlyReading": "Aucun livre en cours",
+  "dashboard.noRecentlyRead": "Aucun livre lu récemment",
 
   // Books page
   "books.title": "Livres",