feat(form-builder): ApplyBindings listener chain with two-transaction pattern (WS-6)

ApplyBindingsOnFormSubmit (sync) wraps the applicator in DB::transaction
and writes apply_status post-commit. On exception: outer catch records
FormSubmissionActionFailure in a separate transaction (survives inner
rollback), marks apply_status=failed, swallows so siblings keep running
(RFC Q3, Q4). When ApplyBindings provisions a Person on a previously
no-subject submission, the listener also writes subject_type/subject_id
back so TriggerPersonIdentityMatchOnFormSubmit (next sync listener) can
find the freshly-provisioned subject.

ApplyBindingsOnFormSectionSubmitted (queued, feature-flagged) ready
for ARTIST_ADVANCE activation per RFC Q10.

Listener chain on FormSubmissionSubmitted explicitly registered in
AppServiceProvider::boot for deterministic ordering (RFC Q1):
ApplyBindings → IdentityMatch → queued siblings.

FormBindingApplicator dropped 'final readonly' to 'class' so listener
tests can subclass it for throw-path coverage; constructor properties
remain readonly individually.

Refs: RFC-WS-6.md §3 (Q1, Q3, Q4, Q10)

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

api/config/form_builder.php

@@ -71,4 +71,17 @@ return [
         'retention_job' => false,  // scheduler task later
     ],
 
+    /**
+     * RFC-WS-6 §3 (Q10) — section-level binding apply runtime gate.
+     *
+     * REMOVAL TRIGGER: enable when ARTIST_ADVANCE feature work begins
+     * (post-S5). At enablement: set FORM_BUILDER_SECTION_APPLY=true,
+     * write section-scoped tests, activate the dispatch path in
+     * FormSubmissionService, remove this flag and the early-return
+     * guard from ApplyBindingsOnFormSectionSubmitted::handle().
+     *
+     * Tracking: BACKLOG.md → ARTIST-ADV-SECTION-APPLY
+     */
+    'section_apply_enabled' => env('FORM_BUILDER_SECTION_APPLY', false),
+
 ];