As suggested during the review of PR #10077, the preference key used for the “Expand all folders by default” setting should be renamed to better match its corresponding title.

However, this preference is already in use by existing users, which means renaming the key outright would cause their saved value to be lost. To avoid breaking existing behavior, we need to introduce a migration strategy.

Tasks:

• Define a new, clearer key name that aligns with the setting title.
• Implement a migration step that:
  • Reads the value stored under the old key.
  • Writes it into the new key.
  • Removes (or safely ignores) the old key afterward.
• Update all references to use the new key.
• Verify preference loading and default values behave as expected after migration.