feat(stats): add word exclusion list for vocabulary tab

- useExcludedWords hook manages excluded words in localStorage
- ExclusionManager modal for viewing/removing excluded words
- Exclusion button on WordDetailPanel header
- Filtered words affect stat cards, charts, frequency table, and word list

stats/src/hooks/useExcludedWords.ts

@@ -0,0 +1,83 @@
+import { useCallback, useSyncExternalStore } from 'react';
+
+export interface ExcludedWord {
+  headword: string;
+  word: string;
+  reading: string;
+}
+
+const STORAGE_KEY = 'subminer-excluded-words';
+
+function toKey(w: ExcludedWord): string {
+  return `${w.headword}\0${w.word}\0${w.reading}`;
+}
+
+let cached: ExcludedWord[] | null = null;
+let cachedKeys: Set<string> | null = null;
+const listeners = new Set<() => void>();
+
+function load(): ExcludedWord[] {
+  if (cached) return cached;
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY);
+    cached = raw ? JSON.parse(raw) : [];
+  } catch {
+    cached = [];
+  }
+  return cached!;
+}
+
+function getKeySet(): Set<string> {
+  if (cachedKeys) return cachedKeys;
+  cachedKeys = new Set(load().map(toKey));
+  return cachedKeys;
+}
+
+function persist(words: ExcludedWord[]) {
+  cached = words;
+  cachedKeys = new Set(words.map(toKey));
+  localStorage.setItem(STORAGE_KEY, JSON.stringify(words));
+  for (const fn of listeners) fn();
+}
+
+function getSnapshot(): ExcludedWord[] {
+  return load();
+}
+
+function subscribe(fn: () => void): () => void {
+  listeners.add(fn);
+  return () => listeners.delete(fn);
+}
+
+export function useExcludedWords() {
+  const excluded = useSyncExternalStore(subscribe, getSnapshot);
+
+  const isExcluded = useCallback(
+    (w: { headword: string; word: string; reading: string }) => getKeySet().has(toKey(w)),
+    [excluded],
+  );
+
+  const toggleExclusion = useCallback(
+    (w: ExcludedWord) => {
+      const key = toKey(w);
+      const current = load();
+      if (getKeySet().has(key)) {
+        persist(current.filter(e => toKey(e) !== key));
+      } else {
+        persist([...current, w]);
+      }
+    },
+    [],
+  );
+
+  const removeExclusion = useCallback(
+    (w: ExcludedWord) => {
+      persist(load().filter(e => toKey(e) !== toKey(w)));
+    },
+    [],
+  );
+
+  const clearAll = useCallback(() => persist([]), []);
+
+  return { excluded, isExcluded, toggleExclusion, removeExclusion, clearAll };
+}