* feat(cli): extend `ktx connection test` to every supported driver
Dispatch by driver: native DBs now call `connector.testConnection()`
(was `introspect(dryRun)`), looker/notion/metabase hit their auth
endpoints, and dbt/metricflow/lookml run `git ls-remote` via the
existing `testRepoConnection` helper. Unknown drivers exit 1 with a
listing of supported ones.
* feat(cli): add `ktx connection test --all` summary list
Tests every configured connection in parallel and renders a single
Clack-style list (◇/│/◆/└, green ✓ / red ✗) consistent with sl list,
with per-row detail and a passed/failed footer. Exits non-zero if any
connection fails. Single-id `ktx connection test` output is preserved.
* fix(cli): read metabase status url from api_url
`ktx status` was probing `url` / `base_url` on metabase connections, but
ktx.yaml stores it as `api_url`, so the field always reported "url not
set". Read `api_url` directly and align the warning text with the actual
key.
