feat(perf): performance composables for lazy loading, dedup, prefetch, cleanup (M18.1-M18.8)

- Image lazy loading: IntersectionObserver + blur-up placeholder
- Request deduplication: in-flight Promise sharing by URL+body key
- Prefetch on hover: 5-minute cache for pre-fetched detail data
- Memory leak audit: useCleanup() tracks intervals/listeners/observers
- Background sync queue: retry failed IDB saves on visibility change
- Bundle splitting: composable architecture enables tree-shaking

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/app/src/composables/useSyncQueue.ts

@@ -0,0 +1,90 @@
+import { ref, onMounted, onUnmounted } from 'vue'
+
+const STORAGE_KEY = 'aiui-sync-queue'
+
+interface QueuedOperation {
+  id: string
+  type: string
+  data: unknown
+  createdAt: number
+}
+
+const queue = ref<QueuedOperation[]>([])
+const hasQueuedItems = ref(false)
+
+function loadQueue() {
+  try {
+    const stored = localStorage.getItem(STORAGE_KEY)
+    if (stored) queue.value = JSON.parse(stored)
+    hasQueuedItems.value = queue.value.length > 0
+  } catch { /* ignore */ }
+}
+
+function saveQueue() {
+  localStorage.setItem(STORAGE_KEY, JSON.stringify(queue.value))
+  hasQueuedItems.value = queue.value.length > 0
+}
+
+loadQueue()
+
+export function useSyncQueue() {
+  function enqueue(type: string, data: unknown) {
+    queue.value.push({
+      id: crypto.randomUUID(),
+      type,
+      data,
+      createdAt: Date.now(),
+    })
+    saveQueue()
+  }
+
+  async function processQueue(handler: (op: QueuedOperation) => Promise<boolean>) {
+    const remaining: QueuedOperation[] = []
+    for (const op of queue.value) {
+      try {
+        const success = await handler(op)
+        if (!success) remaining.push(op)
+      } catch {
+        remaining.push(op)
+      }
+    }
+    queue.value = remaining
+    saveQueue()
+  }
+
+  function clearQueue() {
+    queue.value = []
+    saveQueue()
+  }
+
+  // Auto-retry on visibility change
+  let retryHandler: (() => void) | null = null
+
+  function startAutoRetry(handler: (op: QueuedOperation) => Promise<boolean>) {
+    retryHandler = () => {
+      if (document.visibilityState === 'visible' && queue.value.length > 0) {
+        processQueue(handler)
+      }
+    }
+    document.addEventListener('visibilitychange', retryHandler)
+  }
+
+  onMounted(() => {
+    // Already loaded
+  })
+
+  onUnmounted(() => {
+    if (retryHandler) {
+      document.removeEventListener('visibilitychange', retryHandler)
+    }
+  })
+
+  return {
+    queue,
+    hasQueuedItems,
+    enqueue,
+    processQueue,
+    clearQueue,
+    startAutoRetry,
+  }
+}