Prevent empty passphrases when restoring local chat backups

[eyedol]

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• Pixel 8 Pro, Android 15
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Description

Introduces PassphraseDialogManager to handle the display and input of the backup passphrase dialog. This centralizes the passphrase dialog logic, improves code organization, and allows for easier management of error states and input validation. Updates RestoreLocalBackupFragment to use the new PassphraseDialogManager. Enables the dialog positive button only when input is not blank. Shows error on the text input when a blank passphrase is entered.

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