[LOC] Get off localization-v2

Now that everyone is off the old localization format, we need to get rid of the `-v2` moniker.

## Criteria of acceptance
1. `localization-v2` should be moved to `localization`
2. We should gracefully fall back to v2.
3. Update the "zero-config" file in DA.

Search the repository for references to `localization-v2`, then inspect the zero-config file in DA. Trace how the current localization value is selected and where fallback behavior is handled. Done means the canonical name is `localization`, v2 fallback remains graceful, and the DA zero-config file is updated.

Written by the indexing model from the issue text.