feat(gardens): sortable Deploy column via lateral join
Name the lateral-join binding `:latest_deployment` and expose
`deploy_result` as a Flop join_field sourced from it, then wire the
Gardens index Deploy column to that field so headers become sort links.
Sort order is the raw enum string (alphabetic: failure, partial,
success), not by severity. Gardens with no deployment use Postgres
defaults (NULLs last on ASC, first on DESC).
sow-178
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>