CLI: no way to delete a kind:30617 repo announcement — add `buzz repos delete` emitting an a-tag-only kind:5

[bradleg1]

Problem

There is no way to delete a NIP-34 repo announcement (kind:30617), from the CLI or from Desktop.

Scenario: an agent announced repos with buzz repos create; the repos were later re-announced under the human owner's identity (agents guidance recommends owner-held announcements). The agent's original announcements are now stale duplicates that cannot be removed by anyone:

• Desktop: delete is greyed out for the human because Desktop signs as the human, who is not the author of the agent's events — correct behaviour, but it leaves no path.
• buzz repos …: has create / get / list / bind / protect — no delete.
• buzz messages delete: rejects kind:30617 — it requires an h tag to resolve a channel, and repo announcements don't carry one.
• buzz notes rm: hardcodes the coordinate to 30023:<pubkey>:<slug>, so it can't target 30617.

The author-agent stripped its announcements to inert tombstones (no clone/web URL, no buzz-channel binding), which is the best available mitigation, but the records remain as clutter in the repos panel.

The relay already supports the needed mechanism

buzz notes rm --help documents an a-tag-only NIP-09 kind:5 coordinate soft-delete (deliberately omitting the e tag, since an e tag would route around the relay's coordinate soft-delete). A repo announcement is an addressable event just like a note — the same mechanism applies; only the CLI surface is missing.

Proposal

buzz repos delete --id <d-tag>

emitting kind:5 with a = 30617:<signer-pubkey>:<d-tag> (a-tag-only, mirroring notes rm), restricted to the caller's own announcements. A read-before-write NotFound for a nonexistent coordinate would match notes rm ergonomics.

Observed on Buzz Desktop 0.5.11 (bundled CLI), Linux x86_64.