#10: repo rename/transfer: the API shipped but the CLI half was dropped in the !120 merge

What happened

MR rickub/rickub!120 shipped repo rename and transfer across both halves:
the API (web/api_repos.go) and the CLI (cli/cmd/repo.go). When it was landed,
cli/ had moved to this repository, so the merge hit five modify/delete
conflicts — all under cli/. They were resolved by dropping the CLI half.
The API half merged cleanly and is live.

So the server supports rename and transfer today, and rickub cannot call it.

Where the work is

It is not lost, but it is only in history — commit 4a5d5d2 on
rickub/rickub (feat(web): repo rename and transfer over the API and CLI (#131)):

cli/cmd/repo.go               |  69 ++++++++++++++-
cli/cmd/repo_test.go          |  85 ++++++++++++++++++
cli/internal/api/endpoints.go |  15 +++
cli/internal/api/models.go    |  10 +++

Recover with git show 4a5d5d2 -- cli/ against a rickub/rickub checkout.

Impact

This is filed because the only record was a comment on a merged MR, and a
comment on a merged MR is invisible to anyone who was not in the room. The
predictable outcome is that someone re-implements repo rename from the OpenAPI
spec in six months without ever finding 4a5d5d2 — paying twice for work that is
already written and already had tests (cli/cmd/repo_test.go, 85 lines).

The endpoints are already documented in docs/api/openapi.yaml (also from that
commit), so the CLI is the only missing piece.

Acceptance criterion

rickub repo rename <owner/name> <new-name> and
rickub repo transfer <owner/name> <new-owner> exist, call the live API
endpoints, and carry cli/cmd/repo_test.go's cases forward. Port from 4a5d5d2
rather than rewriting — the tests came with it.

Cross-reference: rickub/rickub!120, and FEATURES.md was corrected on merge (it
had claimed these commands ship).

repo rename/transfer: the API shipped but the CLI half was dropped in the !120 merge — port it from 4a5d5d2 #10

What happened

Where the work is

Impact

Acceptance criterion