fix: hash scheduler-k3s cron-id label to fit Kubernetes' 63-byte cap

The `dokku.com/cron-id` label could exceed Kubernetes' 63-byte cap because the cron ID is `base36(appName === command === schedule)`, which expands roughly 1.5x per byte. The label is now keyed `dokku.com/cron-hash` and holds the `sha1` hex digest of the cron-id, a fixed 40-character value that always fits the cap. The same hex digest is mirrored into the `dokku.com/cron-hash` annotation, and the original base36 cron-id stays in the `dokku.com/cron-id` annotation that `cron:list` reads when surfacing user-facing IDs. Per-task lookups stay server-side via label selectors, so `cron:set --maintenance` and the forbid/replace concurrency checks on `dokku run --cron-id` keep working without any in-memory filtering.

tests/unit/builder-pack.bats

@@ -265,7 +265,7 @@ teardown() {
   echo "output: $output"
   echo "status: $status"
   assert_success
-  assert_output "['task.py']"
+  assert_output "['task.py', 'some', 'cron', 'task']"
 }
 
 @test "(builder-pack) cron:run with Procfile reference" {