feat(form-builder): add FormSubmissionActionFailure model + apply_status casts (WS-6)

- FormSubmissionActionFailure: audit model, no organisation_id (FK-chain
  tenancy per RFC V3), open/resolved/dismissed scopes, canBeRetried()
  helper. Morph alias 'form_submission_action_failure' registered for
  future activity-log subject references.
- FormSubmission: apply_status (ApplyStatus enum cast),
  apply_completed_at (datetime), actionFailures() HasMany,
  scopePendingApply().

Refs: RFC-WS-6.md §3 (Q5), §4 (V3)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/app/Providers/AppServiceProvider.php

@@ -230,6 +230,7 @@ class AppServiceProvider extends ServiceProvider
             'form_submission' => FormSubmission::class,
             'form_submission_section_status' => FormSubmissionSectionStatus::class,
             'form_submission_delegation' => FormSubmissionDelegation::class,
+            'form_submission_action_failure' => \App\Models\FormBuilder\FormSubmissionActionFailure::class,
             'form_value' => FormValue::class,
             'form_value_option' => FormValueOption::class,
             'form_template' => FormTemplate::class,