feat: pull-to-refresh on Home and Library

iOS standalone PWAs don't get Safari's native pull-to-refresh, so add
our own. New <PullToRefresh> component handles the gesture: dampened
drag past an 80px threshold triggers an async onRefresh; below that it
springs back. Swipe direction is locked to the first 6px of movement,
so horizontal carousel swipes (landscape Home) don't accidentally fire
PTR. The arrow icon rotates from 0° to 180° as the pull approaches the
threshold and turns primary-color when ready; during refresh a CSS
spinner replaces it.

- HomeView refreshes the device list (and sync status with it)
- LibraryView refreshes images, pending-share count, devices, and the
  active shared sub-tab page when it's the one in view

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/views/LibraryView.vue

@@ -1,5 +1,6 @@
 <template>
   <main class="library">
+    <PullToRefresh :is-at-top="isAtTop" :on-refresh="refreshLibrary">
     <!-- Tabs -->
     <div class="library__tabs" role="tablist">
       <button
@@ -184,6 +185,7 @@
         >Next →</button>
       </div>
     </template>
+    </PullToRefresh>
 
     <!-- Share sheet -->
     <ShareSheet v-if="shareImageId !== null" v-model="shareSheetOpen" :image-id="shareImageId!" />
@@ -213,6 +215,7 @@ import BaseBottomSheet from '@/components/BaseBottomSheet.vue'
 import BaseButton from '@/components/BaseButton.vue'
 import ApproveCard from '@/components/ApproveCard.vue'
 import ShareSheet from '@/components/ShareSheet.vue'
+import PullToRefresh from '@/components/PullToRefresh.vue'
 import type { Device, Image, SharedImage } from '@/types'
 
 const router       = useRouter()
@@ -288,6 +291,21 @@ onMounted(() => {
   if (activeTab.value === 'shared') loadShared(sharedTab.value)
 })
 
+// ── Pull-to-refresh ───────────────────────────────────────────────────────────
+
+function isAtTop(): boolean {
+  return window.scrollY === 0
+}
+
+async function refreshLibrary() {
+  await Promise.all([
+    imagesStore.fetchImages(),
+    imagesStore.fetchPendingCount(),
+    devicesStore.fetchDevices(),
+    activeTab.value === 'shared' ? loadShared(sharedTab.value, sharedPage.value) : Promise.resolve(),
+  ])
+}
+
 // For now "mine" and "all" show the same list; shared is a placeholder
 const visibleImages = computed(() => imagesStore.images)