feat(scope): declarative FK-chain strategy for OrganisationScope, register on 14 models per addendum Q2 + D-03/D-04

Refactors OrganisationScope to support a declarative, recursive FK-chain
resolver and registers the scope on 14 models that previously relied on
caller-discipline for tenant isolation.

Scope resolver (app/Models/Scopes/OrganisationScope.php):
Models now declare their strategy via:

    public static function tenantScopeStrategy(): array
    {
        return ['column' => 'organisation_id'];           // terminal
        // OR
        return ['via' => FormSchema::class, 'fk' => 'form_schema_id'];
    }

The apply() path walks the chain recursively, building whereIn subqueries
against parent models until it hits a column-based strategy. Max 3 hops;
deeper chains raise App\Exceptions\TenantScopeResolutionException. The
walker accepts BOTH the new tenantScopeStrategy() and the legacy
$organisationScopeColumn property at every hop — so PersonIdentityMatch
can chain via Person, which still uses the legacy event_id bridge, without
requiring Person/Event/Shift/FestivalSection/TimeSlot to migrate to the
new convention in this work package. That migration is a separate
backlog ticket — explicitly scope-controlled per the addendum.

Fourteen newly-scoped models:

  Form-builder child models (D-03):
    FormSchemaSection             via FormSchema                    (1 hop)
    FormField                     via FormSchema                    (1 hop)
    FormSubmission                column organisation_id (Commit 2)
    FormValue                     via FormSubmission                (1 hop)
    FormValueOption               via FormValue -> FormSubmission   (2 hops)
    FormSubmissionSectionStatus   via FormSubmission                (1 hop)
    FormSubmissionDelegation      via FormSubmission                (1 hop)
    FormSchemaWebhook             via FormSchema                    (1 hop)
    FormWebhookDelivery           via FormSubmission                (1 hop)

  Event-data models (D-04 event-data subset):
    ShiftAssignment               via Shift (legacy festival_section_id)
    ShiftWaitlist                 via Shift
    VolunteerAvailability         via TimeSlot (legacy event_id)
    PersonSectionPreference       via FestivalSection (legacy event_id)
    PersonIdentityMatch           via Person (legacy event_id)

Note — task directive specified VolunteerAvailability "via: Event, fk: event_id",
but the table has no event_id column (only person_id + time_slot_id).
Rerouted via TimeSlot, which carries the legacy event_id bridge; same
end result, correct FK.

Security-relevant callers made explicit:
  PublicFormSchemaResource::toArray() now eagerly loads fields + sections
  with withoutGlobalScope(OrganisationScope::class). Prior to this commit
  the public form endpoint silently relied on those relations being
  unscoped. The PublicFormCrossOrgScopeTest pre-existing assertions still
  pass — behaviour unchanged, intent now explicit.

Test fix: FormSchemaApiTest::test_publish_sets_is_published_true was
flaky (factory randomly picked EVENT_REGISTRATION which requires
bindings). Pinned to USER_PROFILE for determinism; PurposeSchemaLifecycleTest
covers the binding-enforcement path.

Test flip: MultiTenancyTest::test_form_schema_webhook_is_not_globally_scoped
renamed to is_scoped_via_fk_chain and asserts the new behaviour: scope
filters by route org, withoutGlobalScope() still exposes cross-org rows.
The test's original purpose ("pin current behaviour so a future refactor
is intentional") is now satisfied by Commit 3 being that intentional
refactor.

Docs:
  SCHEMA.md §3.5.11 Rule 5 — tenantScopeStrategy() convention documented;
    the 14 newly-scoped models enumerated; link to addendum Q2.
  ARCH-FORM-BUILDER.md §4.14 — new section "Multi-tenancy scope chain"
    with the hop-count table for all 14 chains and the withoutGlobalScope
    pattern for cross-org callers.

Tests: tests/Feature/MultiTenancy/ScopeLeakageTest.php — two orgs with
fully-populated record chains down to each of the 14 leaf models; asserts
scoped queries never cross, withoutGlobalScope still does. Plus: three-
hop chain (FormValueOption) explicitly exercised, legacy-column bridge
verified, over-deep chain raises TenantScopeResolutionException. 16 tests /
31 new assertions. Full suite: 1000 passed (2706 assertions).

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

api/app/Http/Resources/FormBuilder/PublicFormSchemaResource.php

@@ -31,7 +31,14 @@ final class PublicFormSchemaResource extends JsonResource
      */
     public function toArray(Request $request): array
     {
-        $this->resource->loadMissing(['fields', 'sections']);
+        // Public endpoints must resolve cross-org — skip OrganisationScope
+        // on the FormField / FormSchemaSection relations (both registered
+        // via addendum Q2 / WS-4 Commit 3). The schema-level tenant check
+        // already happens at PublicFormTokenResolver::resolve().
+        $this->resource->loadMissing([
+            'fields' => fn ($q) => $q->withoutGlobalScope(OrganisationScope::class),
+            'sections' => fn ($q) => $q->withoutGlobalScope(OrganisationScope::class),
+        ]);
 
         $visibleFields = $this->fields
             ->filter(fn ($f) => (bool) $f->is_portal_visible && ! (bool) $f->is_admin_only)