test(forms): model tests, multi-tenancy, migration rollback (Phase 9)

UserProfileTest: belongs-to user, fillable/non-fillable boundaries,
settings cast, lastSubmittedAt accessor (null + max from user-subject
submissions only, ignoring drafts and is_test rows).

FormSchemaTest: ULID PK, OrganisationScope filtering, polymorphic owner
resolution to Event, purpose enum cast, hasMany fields/submissions, and
logSchemaChange() actually creates an activity-log entry.

FormFieldTest: belongs-to schema, field_type stored as string (not DB
enum), binding/translations array casts, hasMany values, soft-delete
preserves historical values, logFieldChange() creates an entry.

FormSubmissionTest: belongs-to schema, polymorphic subject resolution,
status enum cast, schema_snapshot array cast, hasMany values.

FormValueTest: belongs-to submission/field, value array cast, hasMany
options pivot rebuilt by observer, unique-pair DB constraint enforced.

MultiTenancyTest: OrganisationScope correctly filters FormSchema /
FormTemplate / FormFieldLibrary by route-resolved organisation. Pins
the FormSchemaWebhook un-scoped behaviour explicitly so a future scope
addition is an intentional decision, not an accident.

MigrationRollbackTest (group 'slow'): full migrate:fresh → rollback 14
S1 steps → assert all 13 form-builder tables dropped + legacy tables
intentionally retained → re-migrate and assert table list matches
snapshot. Plus a separate test exercising the populate-user-profiles
migration's down().

Supporting tweaks:
- UserProfile::lastSubmittedAt accessor now returns Carbon|null instead
  of a raw timestamp string — testable, and matches Eloquent convention.
- UserProfileFactory cooperates with UserObserver via newModel override
  (updates the auto-created row instead of inserting a duplicate).
- AppServiceProvider morph map extended with all 12 form-builder model
  keys so logSchemaChange/logFieldChange resolve under enforceMorphMap.

Suite: 945 passed (was 911), 2671 assertions.

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

api/app/Models/UserProfile.php

@@ -50,12 +50,16 @@ final class UserProfile extends Model
     protected function lastSubmittedAt(): Attribute
     {
         return Attribute::make(
-            get: fn () => FormSubmission::query()
-                ->where('subject_type', 'user')
-                ->where('subject_id', $this->user_id)
-                ->where('status', FormSubmissionStatus::SUBMITTED)
-                ->where('is_test', false)
-                ->max('submitted_at'),
+            get: function () {
+                $raw = FormSubmission::query()
+                    ->where('subject_type', 'user')
+                    ->where('subject_id', $this->user_id)
+                    ->where('status', FormSubmissionStatus::SUBMITTED)
+                    ->where('is_test', false)
+                    ->max('submitted_at');
+
+                return $raw === null ? null : \Illuminate\Support\Carbon::parse($raw);
+            },
         );
     }
 }