fix(mobile): fix shared file upload hanging by copying to cache

Files shared via iOS Share Sheet / "Open In…" may reference paths
outside the app's sandbox or use security-scoped URLs that React
Native's fetch cannot read. This caused uploads to hang indefinitely
with a spinning indicator.

Fixes:
- Set LSSupportsOpeningDocumentsInPlace to false so iOS copies shared
  files to the app's accessible Inbox directory
- Use expo-file-system to copy external file:// URIs to the app's
  cache directory before uploading (ensureLocalUri helper)
- Apply ensureLocalUri to both initial uploads and retries

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

mobile/app.json

@@ -24,7 +24,7 @@
         "NSPhotoLibraryAddUsageDescription": "DocuElevate saves scanned documents to your photo library.",
         "UIBackgroundModes": ["remote-notification"],
         "ITSAppUsesNonExemptEncryption": false,
-        "LSSupportsOpeningDocumentsInPlace": true,
+        "LSSupportsOpeningDocumentsInPlace": false,
         "CFBundleDocumentTypes": [
           {
             "CFBundleTypeName": "All Documents",