feat(12.2-01): add deferred:purge, its daily framework schedule and relation child hooks

- deferred:purge [--days] in lagoon.RuntimeCommands (purge_days, default 5)
- lagoon.FrameworkSchedule entry at purge_at (default 03:00, empty disables)
- conga prepends framework entries as summercms.lagoon[i]:<command>
- pact.Relation{Before,After}{Create,Update,Delete} optional hooks
- lagoon, conga and pact READMEs, scheduling and setup docs

docs/console/setup-and-maintenance.md

@@ -24,6 +24,21 @@ Every application binary carries the framework's runtime commands. The examples
 
 Each plugin keeps its own migration history table, so rolling back one plugin never touches another. The migrations are listed in [lagoon](../../modules/lagoon/README.md).
 
+## Pending uploads and related records
+
+An admin form holds the files uploaded and the related records created for a record that is not saved yet as deferred bindings. Saving the record commits them; abandoned ones are removed by `deferred:purge`:
+
+| Command | Flags | Purpose |
+|---------|-------|---------|
+| `deferred:purge` | `--days <n>` | Deletes deferred bindings older than `n` days, the unattached uploads they hold and the records created under deferral, and prints the counts. Records that were only linked are kept. Without the flag, `database.deferred_bindings.purge_days` applies, else 5 days. |
+
+```sh
+./bin/acme deferred:purge
+./bin/acme deferred:purge --days=1
+```
+
+The scheduler already runs it every day at 03:00; see [Task scheduling](../plugins/scheduling.md#the-frameworks-own-schedule).
+
 ## Application key
 
 | Command | Flags | Purpose |