feat(stats): persist trend title visibility and add per-chart title limit

Hidden-title selections in the Trends tab now survive relaunches via
localStorage, and a 'Top N per chart' selector (All/3/5/7/10, also
persisted) restores the old top-N declutter behavior on demand.

stats/src/components/trends/anime-visibility.ts

@@ -1,5 +1,62 @@
 import type { PerAnimeDataPoint } from './StackedTrendChart';
 
+const HIDDEN_TITLES_KEY = 'subminer-stats-trends-hidden-titles';
+const MAX_TITLES_KEY = 'subminer-stats-trends-max-titles';
+
+export const MAX_TITLES_OPTIONS = [3, 5, 7, 10] as const;
+
+function getStorage(): Storage | null {
+  try {
+    return globalThis.localStorage ?? null;
+  } catch {
+    return null;
+  }
+}
+
+export function loadHiddenTitles(): Set<string> {
+  try {
+    const raw = getStorage()?.getItem(HIDDEN_TITLES_KEY);
+    const parsed: unknown = raw ? JSON.parse(raw) : [];
+    if (!Array.isArray(parsed)) return new Set();
+    return new Set(parsed.filter((value): value is string => typeof value === 'string'));
+  } catch {
+    return new Set();
+  }
+}
+
+export function saveHiddenTitles(hidden: ReadonlySet<string>): void {
+  try {
+    getStorage()?.setItem(HIDDEN_TITLES_KEY, JSON.stringify([...hidden]));
+  } catch {
+    // Storage can be blocked in private/restricted contexts; keep the in-memory choice.
+  }
+}
+
+export function loadMaxTitles(): number | null {
+  try {
+    const raw = getStorage()?.getItem(MAX_TITLES_KEY);
+    if (raw === null || raw === undefined) return null;
+    const value = Number(raw);
+    return Number.isInteger(value) && value > 0 ? value : null;
+  } catch {
+    return null;
+  }
+}
+
+export function saveMaxTitles(value: number | null): void {
+  try {
+    const storage = getStorage();
+    if (!storage) return;
+    if (value === null) {
+      storage.removeItem(MAX_TITLES_KEY);
+    } else {
+      storage.setItem(MAX_TITLES_KEY, String(value));
+    }
+  } catch {
+    // Storage can be blocked in private/restricted contexts; keep the in-memory choice.
+  }
+}
+
 export function buildAnimeVisibilityOptions(datasets: PerAnimeDataPoint[][]): string[] {
   const totals = new Map<string, number>();
   for (const dataset of datasets) {