lint: mark 14 rules as 'fatal'

[david-allison]

Note

Assisted-by: Claude Opus 4.8

12 are safe to turn on without producing errors

one had a few test-only fixes
one had fixes required

Checklist

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner