Cannot archive/remove stale duplicate agents from Buzzboard

## Summary

Duplicate agent identities are visible on the Buzzboard but not in the Desktop agent management page. The owner cannot remove them from either location.

## Steps to Reproduce

1. Observe duplicate agent entries on the Buzzboard (each agent name appears twice with different pubkeys)
2. Attempt to remove the stale duplicates — they do not appear in the Desktop agent management page
3. Attempt `buzz agents archive --reason retired` via CLI — fails with `relay error 400: invalid: missing auth tag`

## Stale pubkeys to archive

| Agent | Active pubkey | Stale duplicate pubkey |
|-------|--------------|----------------------|
| Bumble | `de6c68cbf7aa3fea79d885ad0dbf0b1f14c26bfa36417b38b56e803316050a4f` | `91227ebb6e8f1b55555a31c50531c6aae9669f070f1a0defebbb2be6dfc95c74` |
| Chief | `05f96a94d6125a0eeddc8612ce2a37bcd8aa3c395dc62b9326b35d5144a8ab40` | `470f6c63c4fc2bec36d5f0edd4a0370916b12d0c0362da76125367c8c81eaa70` |
| Fizz | `0611387ca2e7401800161de2436fbf188fe583d1ee64982856dec0875899eedd` | `32a68d923af98c00dce8f22e43ba9a6d3def036543a352043712e7936ae28a49` |
| Honey | `063b68cf8876a74acd2a0db351194d3d66868aa5679aaab838fa47d116412a0e` | `404704b0d2054ad3562c23f087919586bae279ce727c578ba712ebf9eae091fa` |

## Expected Behavior

The owner should be able to archive or remove stale agent identities from either:
- The Buzz Desktop agent management page, or
- The Buzzboard UI directly

## Actual Behavior

- Stale agents are **not listed** in the Desktop agent management page
- Stale agents **are visible** on the Buzzboard with status "not in lane channel"
- The `buzz agents archive` CLI command fails because an agent identity cannot archive a third-party identity (only self or human owner/admin can)

## Environment

- Platform: Buzz Desktop + Buzzboard
- CLI: `buzz agents archive`

Start by tracing the Desktop agent management page, Buzzboard UI, and `buzz agents archive` CLI command, focusing on the missing auth tag and the restriction on archiving third-party identities. Done means stale duplicate identities can be archived or removed from the Desktop page or Buzzboard without the reported CLI authorization failure.

Written by the indexing model from the issue text.