refactor(persist): one per-domain persist scheduler

stores/persist.ts: createPersistScheduler — trailing-edge debounce,
flush, per-domain isolation. search-history writes collapse from
per-keystroke to one debounced write; scope save stays direct.

src/stores/persist.ts

@@ -0,0 +1,57 @@
+/**
+ * Persistence scheduler for PodTUI
+ * Per-domain trailing-edge debounced writes
+ */
+
+/** Debounced writer: rapid schedules collapse into one write per domain. */
+export interface PersistScheduler {
+	/** Mark a domain dirty and (re)arm its trailing-edge write timer. */
+	schedule(domain: string): void;
+	/** Write the domain immediately if dirty; cancels any pending timer. */
+	flush(domain: string): void;
+	/** Write every dirty domain immediately. */
+	flushAll(): void;
+}
+
+/** Timer handle as returned by setTimeout in this runtime. */
+type TimerHandle = ReturnType<typeof setTimeout>;
+
+/** Build a per-domain trailing-edge debouncer. `write` is invoked with the
+ *  domain name; callers read current state inside it, so a flush always
+ *  lands the latest value. Rapid schedule() calls share one timer. */
+export function createPersistScheduler(
+	write: (domain: string) => void,
+	debounceMs = 250,
+): PersistScheduler {
+	const dirty = new Set<string>();
+	const timers = new Map<string, TimerHandle>();
+
+	const flush = (domain: string): void => {
+		const timer = timers.get(domain);
+		if (timer) {
+			clearTimeout(timer);
+			timers.delete(domain);
+		}
+		if (!dirty.has(domain)) return;
+		dirty.delete(domain);
+		write(domain);
+	};
+
+	const schedule = (domain: string): void => {
+		dirty.add(domain);
+		clearTimeout(timers.get(domain));
+		timers.set(
+			domain,
+			setTimeout(() => {
+				timers.delete(domain);
+				flush(domain);
+			}, debounceMs),
+		);
+	};
+
+	const flushAll = (): void => {
+		for (const domain of [...dirty]) flush(domain);
+	};
+
+	return { schedule, flush, flushAll };
+}