Localized hardcoded DBus connection error

[google-labs-jules]

Localized hardcoded DBus connection error.

• Added error-connect-dbus key to i18n/en/cosmic_ext_fprint.ftl.
• Added ConnectDbus(String) variant to AppError.
• Updated AppError::localized_message to handle the new variant.
• Updated src/app/mod.rs to use AppError::ConnectDbus instead of AppError::Unknown for connection errors.
• Added unit test test_app_error_localization to verify the localization of the new error.
• Updated Cargo.lock to sync with Cargo.toml.

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PR created automatically by Jules for task 9046609356960233563 started by @jotuel

[google-labs-jules]

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