feat(form-builder): apply_deadline_seconds config key (default 5)

Per RFC-WS-6 §Q1 v1.3 addition 4.

Configurable deadline for FormBindingApplicator::apply(). Default 5
seconds catches the long tail of slow applies before they hang the
public flow. Tunable per environment via FORM_BUILDER_APPLY_DEADLINE_SECONDS.

Consumed by ApplyBindingsOnFormSubmit::handle's withDeadline() call
(landed in Phase B).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

api/config/form_builder.php

@@ -84,4 +84,28 @@ return [
      */
     'section_apply_enabled' => env('FORM_BUILDER_SECTION_APPLY', false),
 
+    /**
+     * FormBindingApplicator deadline in seconds.
+     *
+     * The wrapper around FormBindingApplicator::apply() throws
+     * FormBindingApplicatorTimeoutException if the call takes longer
+     * than this value. The exception is caught by
+     * ApplyBindingsOnFormSubmit's outer transaction handler and recorded
+     * as a form_submission_action_failures row with apply_status=FAILED,
+     * failure_response_code='temporary_error'.
+     *
+     * Default 5 seconds — typical apply() takes <100ms; the deadline
+     * catches the long tail (slow query against a massive person pool,
+     * lock-for-update wait that should have been resolved at the
+     * database level, etc.) before it hangs the public flow.
+     *
+     * Tune upward if a legitimate use-case surfaces (very large schemas
+     * with many bindings against multi-million-row entity tables). Tune
+     * downward if SLO requirements demand stricter response-time
+     * guarantees.
+     *
+     * Per RFC-WS-6 §Q1 v1.3 addition 4.
+     */
+    'apply_deadline_seconds' => env('FORM_BUILDER_APPLY_DEADLINE_SECONDS', 5),
+
 ];