feat: overhaul stats dashboard with navigation, trends, and anime views

Add navigation state machine for tab/detail routing, anime overview
stats with Yomitan lookup rates, session word count accuracy fixes,
vocabulary tab hook order fix, simplified trends data fetching from
backend-aggregated endpoints, and improved session detail charts.

stats/src/components/layout/TabBar.tsx

@@ -1,6 +1,6 @@
 import { useRef, type KeyboardEvent } from 'react';
 
-export type TabId = 'overview' | 'anime' | 'trends' | 'vocabulary' | 'sessions' | 'library';
+export type TabId = 'overview' | 'anime' | 'trends' | 'vocabulary' | 'sessions';
 
 interface Tab {
   id: TabId;
@@ -9,9 +9,8 @@ interface Tab {
 
 const TABS: Tab[] = [
   { id: 'overview', label: 'Overview' },
-  { id: 'anime', label: 'Anime' },
+  { id: 'anime', label: 'Library' },
   { id: 'trends', label: 'Trends' },
-  { id: 'library', label: 'Library' },
   { id: 'vocabulary', label: 'Vocabulary' },
   { id: 'sessions', label: 'Sessions' },
 ];

stats/src/components/layout/Tooltip.tsx

@@ -0,0 +1,22 @@
+interface TooltipProps {
+  text: string;
+  children: React.ReactNode;
+}
+
+export function Tooltip({ text, children }: TooltipProps) {
+  return (
+    <div className="group/tip relative">
+      {children}
+      <div
+        role="tooltip"
+        className="pointer-events-none absolute bottom-full left-1/2 -translate-x-1/2 mb-2 z-50
+          max-w-56 px-2.5 py-1.5 rounded-md text-xs text-ctp-text bg-ctp-surface2 border border-ctp-overlay0 shadow-lg
+          opacity-0 scale-95 transition-all duration-150
+          group-hover/tip:opacity-100 group-hover/tip:scale-100"
+      >
+        {text}
+        <div className="absolute top-full left-1/2 -translate-x-1/2 -mt-px border-4 border-transparent border-t-ctp-surface2" />
+      </div>
+    </div>
+  );
+}