feat: complete hosted mod sync and launcher interface updates

Add pack sync markers, tagged mod updates, parallel progress, JWT downloads and retry recovery. Include pending onboarding, about scene, compatibility data pack and download fixes.

apps/app-frontend/src/composables/useHostedSync.ts

@@ -0,0 +1,37 @@
+import { computed, reactive } from 'vue'
+import { hostedSync, type HostedSyncResult } from '../helpers/hosted-packs.ts'
+
+const tasks = reactive(
+	new Map<string, { busy: boolean; result: HostedSyncResult | null; error: string }>(),
+)
+
+export function useHostedSync(instanceId: () => string) {
+	const task = computed(() => {
+		const id = instanceId()
+		if (!tasks.has(id)) tasks.set(id, { busy: false, result: null, error: '' })
+		return tasks.get(id)!
+	})
+
+	async function sync() {
+		const id = instanceId()
+		const current = task.value
+		if (current.busy) return
+		current.busy = true
+		current.error = ''
+		current.result = null
+		try {
+			current.result = await hostedSync(id)
+		} catch (error) {
+			current.error = String(error)
+		} finally {
+			current.busy = false
+		}
+	}
+
+	return {
+		busy: computed(() => task.value.busy),
+		result: computed(() => task.value.result),
+		error: computed(() => task.value.error),
+		sync,
+	}
+}