Add `buzz repos delete` command to remove repository announcements

## Summary

There is no way to delete a repository announcement (NIP-34, kind 30617) via the Buzz CLI. The `buzz repos` subcommands are limited to `create`, `get`, `list`, and `protect`.

## Use Case

A repository (`newworld-career-search`) was created by an agent on behalf of the owner and is no longer needed. The owner wants to remove it but has no way to do so — neither the CLI nor the Desktop UI offer a delete option for repos.

In Nostr, deletion is handled by publishing a deletion event (NIP-09, kind 5) referencing the target event. The CLI should support this for repo announcements.

## Proposed Solution

Add a `buzz repos delete` command that:
1. Accepts a repo identifier (`--id `)
2. Publishes a NIP-09 deletion event (kind 5) targeting the repo announcement (kind 30617)
3. The relay removes or hides the deleted repo

## Details

- Repo to delete: `newworld-career-search`
- Event ID: `c35e35c0d8e382c29311772f1a80227ba1709b7337648bda865dea965586a8bf`
- Publisher pubkey: `05f96a94d6125a0eeddc8612ce2a37bcd8aa3c395dc62b9326b35d5144a8ab40`
- Owner (auth tag): `12de1381c72e15c2a06eecda7bd0b8186d7d336fb7f27064602f647f619acfc6`

## Interim Request

Please delete the above repo announcement from the `ajeeb.communities.buzz.xyz` relay, as the owner has no self-service path to do so currently.

Start at the existing `buzz repos` entry point and inspect the `create`, `get`, `list`, and `protect` subcommands to find how repository announcements are published. Add the `delete --id ` workflow so it publishes a NIP-09 kind 5 event targeting a kind 30617 announcement; done means the command accepts the identifier and the relay removes or hides the repository.

Written by the indexing model from the issue text.