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/lib/vocabulary-tab.test.ts

@@ -0,0 +1,22 @@
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import path from 'node:path';
+import test from 'node:test';
+
+const VOCABULARY_TAB_PATH = path.resolve(
+  import.meta.dir,
+  '../components/vocabulary/VocabularyTab.tsx',
+);
+
+test('VocabularyTab declares all hooks before loading and error early returns', () => {
+  const source = fs.readFileSync(VOCABULARY_TAB_PATH, 'utf8');
+  const loadingGuardIndex = source.indexOf('if (loading) {');
+
+  assert.notEqual(loadingGuardIndex, -1, 'expected loading early return');
+
+  const hooksAfterLoadingGuard = source
+    .slice(loadingGuardIndex)
+    .match(/\buse(?:State|Effect|Memo|Callback|Ref|Reducer)\s*\(/g);
+
+  assert.deepEqual(hooksAfterLoadingGuard ?? [], []);
+});