feat(mvp): phase 4 - app registry & healthcheck

Add app CRUD API endpoints, healthcheck service with node-cron scheduler,
icon resolver (Lucide, Simple Icons, CDN, uploads), app management UI
with Superforms, health badge component, and Docker health endpoint.

src/lib/server/services/healthcheckService.ts

@@ -0,0 +1,83 @@
+import * as appService from './appService.js';
+import { AppStatusValue } from '$lib/utils/constants.js';
+
+export interface HealthcheckResult {
+	readonly appId: string;
+	readonly status: string;
+	readonly responseTime: number | null;
+}
+
+/**
+ * Perform a health check on a single app by making an HTTP request to its URL.
+ */
+export async function checkAppHealth(app: {
+	readonly id: string;
+	readonly url: string;
+	readonly healthcheckMethod: string;
+	readonly healthcheckExpectedStatus: number;
+	readonly healthcheckTimeout: number;
+}): Promise<HealthcheckResult> {
+	const controller = new AbortController();
+	const timeoutId = setTimeout(() => controller.abort(), app.healthcheckTimeout);
+
+	const start = Date.now();
+
+	try {
+		const response = await fetch(app.url, {
+			method: app.healthcheckMethod,
+			signal: controller.signal,
+			redirect: 'follow',
+			headers: {
+				'User-Agent': 'WebAppLauncher-Healthcheck/1.0'
+			}
+		});
+
+		const responseTime = Date.now() - start;
+
+		const status =
+			response.status === app.healthcheckExpectedStatus
+				? AppStatusValue.ONLINE
+				: AppStatusValue.DEGRADED;
+
+		return { appId: app.id, status, responseTime };
+	} catch (err) {
+		const responseTime = Date.now() - start;
+
+		if (err instanceof DOMException && err.name === 'AbortError') {
+			return { appId: app.id, status: AppStatusValue.OFFLINE, responseTime };
+		}
+
+		return { appId: app.id, status: AppStatusValue.OFFLINE, responseTime: null };
+	} finally {
+		clearTimeout(timeoutId);
+	}
+}
+
+/**
+ * Check all apps that have healthcheck enabled, record their statuses.
+ */
+export async function checkAllApps(): Promise<readonly HealthcheckResult[]> {
+	const targets = await appService.getHealthcheckTargets();
+
+	if (targets.length === 0) {
+		return [];
+	}
+
+	const results = await Promise.allSettled(targets.map((target) => checkAppHealth(target)));
+
+	const outcomes: HealthcheckResult[] = [];
+
+	for (const result of results) {
+		if (result.status === 'fulfilled') {
+			const { appId, status, responseTime } = result.value;
+			try {
+				await appService.recordStatus(appId, status, responseTime);
+			} catch {
+				// Log but don't fail the whole batch
+			}
+			outcomes.push(result.value);
+		}
+	}
+
+	return outcomes;
+}