perf: batch-load app history to eliminate N+1 fetches on board load

Previously each AppWidget fetched /api/apps/{id}/history individually
on mount, causing N sequential HTTP requests. Now the board page
server load fetches all app histories in a single Prisma query via
getBatchStatusHistory() and passes them to AppWidget via Svelte
context. AppWidget uses the pre-loaded data immediately with a
fallback fetch for non-board contexts.

src/lib/server/services/appService.ts

@@ -127,6 +127,38 @@ export async function getStatusHistory(appId: string, limit: number = 50) {
 	});
 }
 
+/**
+ * Batch-fetch status history for multiple apps in a single query.
+ * Returns a map of appId -> { history, uptimePercent }.
+ */
+export async function getBatchStatusHistory(
+	appIds: readonly string[],
+	limitPerApp: number = 288
+): Promise<ReadonlyMap<string, { readonly history: readonly { status: string; responseTime: number | null; checkedAt: Date }[]; readonly uptimePercent: number }>> {
+	if (appIds.length === 0) return new Map();
+
+	const allStatuses = await prisma.appStatus.findMany({
+		where: { appId: { in: [...appIds] } },
+		orderBy: { checkedAt: 'desc' },
+		select: { appId: true, status: true, responseTime: true, checkedAt: true }
+	});
+
+	const result = new Map<string, { history: { status: string; responseTime: number | null; checkedAt: Date }[]; uptimePercent: number }>();
+
+	for (const appId of appIds) {
+		const statuses = allStatuses.filter((s) => s.appId === appId).slice(0, limitPerApp).reverse();
+		const totalChecks = statuses.length;
+		const onlineChecks = statuses.filter((s) => s.status === 'online').length;
+		const uptimePercent = totalChecks > 0 ? Math.round((onlineChecks / totalChecks) * 1000) / 10 : 0;
+		result.set(appId, {
+			history: statuses.map((s) => ({ status: s.status, responseTime: s.responseTime, checkedAt: s.checkedAt })),
+			uptimePercent
+		});
+	}
+
+	return result;
+}
+
 export async function getHealthcheckTargets() {
 	return prisma.app.findMany({
 		where: { healthcheckEnabled: true },