Show MMSI directory CSV validation errors in the UI

[mbof]

Repro steps

1. Connect and open MMSI directory
2. Input a name that is too long (> 16 chars)
3. Click Save

Observed behavior

• Nothing in the UI
• In the console log, error "Error: Name must not be more than 16 characters"

Expected behavior

• The validation error is shown in the UI so that the user knows why nothing happened.
• The validation error indicates the specific line / context so that the user knows which line needs fixing.

[mbof]

YAML has better line number indication, so I'm not sure we'd fix this vs. tell people to use YAML instead.