ottyl/tickets/004-remove-grey-theme-keep-dark.md

Remove duplicate "grey" theme, keep "dark"

Dark and grey are the same thing. Keep dark, remove grey.

Acceptance criteria

• The "grey" theme option is removed from theme selection UI and settings.
• Any references/config values for "grey" are migrated or aliased to "dark" so existing saved settings don't break.
• "dark" remains as the single equivalent theme.