No `get_admin`-style settleing of empty admin set post-recovery regression test

[therealjhay]

ProblemTests cover recovery happy paths but not a recovery that yields an empty/duplicate admin set (validate_admins_and_threshold should reject, but isn't asserted).

1. Empty-set recovery untested.
2. Duplicate admins untested.
3. Guard not pinned.

Solution

• Add tests for empty/duplicate recovery targets.
• Assert validate_admins_and_threshold catches them.

Acceptance Criteria

• Empty/duplicate recovery targets rejected.
• cargo test --workspace passes.

Note for Contributors: Write a clear PR description. Show the duplicate-target test.

[BigManly4]

Hello maintainer, I would love to resolve this issue within few hours. I am a Full-Stack Dev with contributions to Oss projects. Please assign.

[grantfox-oss]

🦊 GrantFox — @BigManly4 has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #582)
2. Your PR will be reviewed by the Betta-Pay maintainers

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