feat(app): add offline mode composable and enhanced PWA caching

Create useOffline.ts with online/offline detection, sync queue for
pending actions, and auto-process on reconnect. Enhance vite PWA config
with CacheFirst for TMDB and Wikipedia images, StaleWhileRevalidate for
TMDB API responses, with size and TTL limits.

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

packages/app/src/composables/useOffline.ts

@@ -0,0 +1,75 @@
+import { ref, onMounted, onUnmounted } from 'vue'
+
+export interface SyncAction {
+  type: string
+  payload: unknown
+  timestamp: number
+}
+
+const isOnline = ref(navigator.onLine)
+const pendingSync = ref(0)
+const syncQueue: SyncAction[] = []
+
+function handleOnline() {
+  isOnline.value = true
+  processSyncQueue()
+}
+
+function handleOffline() {
+  isOnline.value = false
+}
+
+/** Queue an action to be synced when back online */
+function queueForSync(action: SyncAction) {
+  syncQueue.push(action)
+  pendingSync.value = syncQueue.length
+}
+
+/** Process all pending sync actions */
+async function processSyncQueue(): Promise<void> {
+  if (!isOnline.value || syncQueue.length === 0) return
+
+  while (syncQueue.length > 0) {
+    const action = syncQueue.shift()
+    if (!action) break
+
+    try {
+      // Route sync actions based on type
+      if (action.type === 'conversation') {
+        // Conversation sync handled by idb-storage auto-save
+        continue
+      }
+      if (action.type === 'favorite') {
+        // Favorites are local-only, no sync needed
+        continue
+      }
+      // Add more sync handlers as needed
+    } catch {
+      // Re-queue failed actions
+      syncQueue.unshift(action)
+      break
+    }
+  }
+
+  pendingSync.value = syncQueue.length
+}
+
+export function useOffline() {
+  onMounted(() => {
+    window.addEventListener('online', handleOnline)
+    window.addEventListener('offline', handleOffline)
+    isOnline.value = navigator.onLine
+  })
+
+  onUnmounted(() => {
+    window.removeEventListener('online', handleOnline)
+    window.removeEventListener('offline', handleOffline)
+  })
+
+  return {
+    isOnline,
+    pendingSync,
+    queueForSync,
+    processSyncQueue,
+  }
+}

packages/app/vite.config.ts

@@ -70,6 +70,30 @@ export default defineConfig({
             urlPattern: /\/api\/rss-articles\?.*/i,
             handler: 'NetworkOnly',
           },
+          {
+            urlPattern: /\/api\/tmdb\/.*/i,
+            handler: 'StaleWhileRevalidate',
+            options: {
+              cacheName: 'tmdb-cache',
+              expiration: { maxEntries: 200, maxAgeSeconds: 86400 },
+            },
+          },
+          {
+            urlPattern: /^https:\/\/image\.tmdb\.org\/.*/i,
+            handler: 'CacheFirst',
+            options: {
+              cacheName: 'tmdb-images',
+              expiration: { maxEntries: 500, maxAgeSeconds: 604800 },
+            },
+          },
+          {
+            urlPattern: /^https:\/\/upload\.wikimedia\.org\/.*/i,
+            handler: 'CacheFirst',
+            options: {
+              cacheName: 'wiki-images',
+              expiration: { maxEntries: 200, maxAgeSeconds: 604800 },
+            },
+          },
         ],
       },
       devOptions: {