Use the validator admin API as the only private recovery interface

[huitseeker]

#2393 added local commands to export a private record and issue its Golden decryption share. #2407 adds the same recovery flow to a private admin API. Keeping both creates two places for access rules and tests.

Keep the admin API. The recovery UI already needs it, and it can issue a share for another validator's record. After #2407 lands, remove export-private-record and issue-private-record-share. Keep the shared Golden helpers used by the admin service, and move any needed recovery tests to that service.

Blocked by #2407.

[huitseeker]

Note: we introduced a ROWID index in the transaction table in #2407 for the purpose of an admin endpoint listing transactions. As discussed with @Mirko-von-Leipzig may be worth removing as part of this.