feat(linux): make the error details the app writes translatable

[datlechin]

Why

Release criterion 9: no message the user cannot have translated. Error details from the core crates still reached the app as English: CSV import reasons, cell and JSON parse errors, the type and default parsers, the keyring, certificate files and a driver's unsupported feature.

Change

• Core errors carry values instead of English: UnsupportedFeature, a JSON line and column, the CSV line, an io::ErrorKind. The app writes each sentence through gettext.
• A keyring failure shows only the Secret Service's own reply; oo7's text goes to the log.
• An internal driver error shows the app's sentence and logs its detail at trace.
• A CSV file without a header names its fields "Column 1", "Column 2" in the app.

Verified

New tests pin each mapping. Changed on purpose: a_backend_error_keeps_its_detail (now a_backend_error_shows_the_services_words_and_never_oo7s), a_file_with_no_header_gets_names_from_the_positions, the_message_says_what_happened_in_words_not_the_error_text, a_bad_row_names_its_line_in_the_file.