Add a --status filter to `kitebase search`, so
`python -m tickets search sso --status open` shows only open tickets
matching "sso" (today that's KITE-144).

Where to look: search_tickets in tickets/search.py and main in
tickets/cli.py. Valid statuses are STATUSES in tickets/models.py.

Rules (also in AGENTS.md):
- An unknown status raises ValueError in search_tickets, and the command
  shows a clear error instead of a traceback.
- Only change tickets/search.py, tickets/cli.py and files under tests/.
- Add a test for each new behaviour. Don't change what existing tests check.

Done means `python -m pytest -q` passes. Run it and show me the output.
