feat(mobile): mobile UX polish with bottom sheet, haptics, gestures, PWA (M16.1-M16.10)

- BottomSheet.vue: gesture-driven with 40/80/100% snap points, backdrop
- Swipe navigation: left/right to switch conversations, 80px threshold
- Pull-to-refresh: custom glass spinner, haptic on release
- Haptic feedback: useHaptics() composable with pattern presets
- Web Share API: native share with glass fallback sheet
- Pinch-to-zoom: usePinchZoom() composable, 1x-4x, double-tap reset
- iOS PWA: safe area insets CSS utilities, black-translucent status bar
- Long-press context menus: 500ms trigger via bottom sheet
- Scroll position memory: per-route Map, auto-restore on mount
- Landscape mode: CSS split layout, orientation change detection

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

packages/app/src/composables/useWebShare.ts

@@ -0,0 +1,48 @@
+import { ref } from 'vue'
+
+export function useWebShare() {
+  const isSupported = 'share' in navigator
+  const showFallback = ref(false)
+  const fallbackText = ref('')
+  const fallbackUrl = ref('')
+
+  async function share(data: { title?: string; text?: string; url?: string }) {
+    if (isSupported) {
+      try {
+        await navigator.share(data)
+        return true
+      } catch {
+        // User cancelled or not supported
+      }
+    }
+
+    // Fallback: show glass share sheet
+    fallbackText.value = data.text ?? data.title ?? ''
+    fallbackUrl.value = data.url ?? ''
+    showFallback.value = true
+    return false
+  }
+
+  async function copyToClipboard(text: string) {
+    try {
+      await navigator.clipboard.writeText(text)
+      return true
+    } catch {
+      return false
+    }
+  }
+
+  function closeFallback() {
+    showFallback.value = false
+  }
+
+  return {
+    isSupported,
+    showFallback,
+    fallbackText,
+    fallbackUrl,
+    share,
+    copyToClipboard,
+    closeFallback,
+  }
+}