feat(stats): add v1 immersion stats dashboard (#19)

stats/src/hooks/useVocabulary.ts

@@ -0,0 +1,52 @@
+import { useState, useEffect } from 'react';
+import { getStatsClient } from './useStatsApi';
+import type { VocabularyEntry, KanjiEntry } from '../types/stats';
+
+export function useVocabulary() {
+  const [words, setWords] = useState<VocabularyEntry[]>([]);
+  const [kanji, setKanji] = useState<KanjiEntry[]>([]);
+  const [knownWords, setKnownWords] = useState<Set<string>>(new Set());
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    let cancelled = false;
+    setLoading(true);
+    setError(null);
+    const client = getStatsClient();
+    Promise.allSettled([client.getVocabulary(500), client.getKanji(200), client.getKnownWords()])
+      .then(([wordsResult, kanjiResult, knownResult]) => {
+        if (cancelled) return;
+        const errors: string[] = [];
+
+        if (wordsResult.status === 'fulfilled') {
+          setWords(wordsResult.value);
+        } else {
+          errors.push(wordsResult.reason.message);
+        }
+
+        if (kanjiResult.status === 'fulfilled') {
+          setKanji(kanjiResult.value);
+        } else {
+          errors.push(kanjiResult.reason.message);
+        }
+
+        if (knownResult.status === 'fulfilled') {
+          setKnownWords(new Set(knownResult.value));
+        }
+
+        if (errors.length > 0) {
+          setError(errors.join('; '));
+        }
+      })
+      .finally(() => {
+        if (cancelled) return;
+        setLoading(false);
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  return { words, kanji, knownWords, loading, error };
+}