feat(18.1-08): detached admin bulk actions run outside the framework transaction

- pact.AdminBulkAction.Detached (json:"-"): opt-in; records loaded through the list scope without row locks, no write transaction in the context
- cabana BulkAction: detached branch with the same empty, partial-selection, failure and message rules; lockScoped is loadScoped with lock, the locked path unchanged
- docs: admin-controllers bulk route list, pact and cabana READMEs

docs/backend/admin-controllers.md

@@ -444,6 +444,7 @@ The admin SPA shows the declared actions in a "Bulk actions" menu next to the se
 - `Run` writes through `cabana.TxFromContext(ctx)`. Any error rolls every row back; a `cabana.ValidationError` is a 422 and any other error the opaque 500.
 - The action's `Permissions` are checked on top of the controller's. An administrator who may not run an action does not get it in the list schema, and posting it answers 403.
 - `pact.AdminBulkActionResult` carries an optional `Message` (a phrase key or text) and `Affected`, the number of records the action changed. The answer is a `cabana.BulkActionResult`.
+- An action with `Detached: true` runs outside the framework transaction. Its records are loaded through the same scope, with the same empty and 409 rules, but without row locks, and `cabana.TxFromContext` reports no transaction. `Run` opens the short transactions it needs (`lagoon.Transaction`). Set it on an action that calls an external service, so that no transaction or row lock is held across the call. What the action saved before a later failure stays saved.
 
 Bulk actions have their own namespace next to the toolbar and widget actions: a name is unique among the controller's bulk actions, and `create` and `delete` stay reserved. `bulkActions` needs `showCheckboxes: true`. A name the controller does not register, a duplicate, or an action without a label stops the start-up. The built-in bulk delete is not a declared action and keeps its own route and toolbar button.