AutoFill: Cannot save file (On My iPhone)

[keepassium]

Description

When creating a passkey in a database stored in On My iPhone/KeePassium, saving fails with the message:

EN: Cannot save file (On My iPhone)
DE: Datei konnte nicht gespeichert werden (Auf meinem iPhone)

Workaround
Move your database out of "KeePassium" folder. (For example, directly to "On My iPhone".)

• Open the standard iOS Files app, navigate to On My iPhone → KeePassium
• Long-press your database → Move → select "On My iPhone" as destination
• Return to "On My iPhone" and tap the moved file to link it to KeePassium
• After that, saving in AutoFill should work.

How to reproduce
Steps to reproduce the behavior:

1. Create a database in "KeePassium" folder locally on device
2. Open https://passkeys-debugger.io and tap "Create Passkey"
3. Proceed to create a passkey in the created database
4. Observe the error message

Expected behavior
Database should be saved

Environment:

• Device: iPhone 11/13
• OS: iOS 17.7.2 and 18.2
• App Version: 2.0.158

Logged error message

FileAccessError.swift:217 	make(from:fileName:fileProvider:) 	Failed to access the file [
  fileProvider: com.apple.FileProvider.LocalStorage, 
  systemError: 
    Error Domain=NSCocoaErrorDomain 
    Code=513 "You don’t have permission to save the file “sandbox.kdbx” in the folder “Documents”." 
    UserInfo={
      NSFilePath=/private/var/mobile/Containers/Data/Application/_UUID_/Documents/sandbox.kdbx,
      NSUnderlyingError=0x300df6550 {Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted"}
    }]

Context: #297