feat(form-builder): exception hierarchy for binding-apply pipeline

Per RFC-WS-6 §Q3 v1.3 addition 2 (binding hierarchy) + §Q2 (invariant exception).

- Refactored FormBindingApplicatorException from concrete final to abstract
  base. Constructor (submissionId, message, previous?) preserves submissionId
  as a public readonly property so D2's outer-transaction handler can write
  it structurally to form_submission_action_failures.context JSON without
  regex-parsing the message. Replaced public-readonly reasonCode property
  with abstract reasonCode(): string method.
- Added 3 reason-coded subclasses:
  - FormBindingSchemaConfigException -> 'schema_config_error' (422)
  - FormBindingInfraException -> 'temporary_error' (503, NOT final because
    Timeout extends it)
  - FormBindingDataIntegrityException -> 'data_integrity_error' (422)
- Added FormBindingApplicatorTimeoutException extending FormBindingInfraException
  (timeout = temporary infra issue from user perspective; reasonCode inherited).
- Added IdentityMatchInvariantViolation as a sibling DomainException — NOT
  in the FormBindingApplicatorException hierarchy because it's thrown
  outside the binding-applicator pipeline.
- Migrated 3 existing throw sites in FormBindingApplicator::apply():
  - 'no_transaction' -> FormBindingInfraException (developer-error wants
    infra-triage workflow: GlitchTip alert + retry-after)
  - 'no_schema' -> FormBindingSchemaConfigException
  - 'unknown_purpose' -> FormBindingSchemaConfigException
- Updated FormBindingApplicatorIntegrationTest::test_no_transaction_guard_present
  to assert against the new throw shape (FormBindingInfraException + new
  message string) while preserving the test's intent (guard exists in source).

Wiring (deadline wrapper, classifier integration in listener catch +
retry-service recordFailure) lands in D2.

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

api/tests/Feature/FormBuilder/Bindings/FormBindingApplicatorIntegrationTest.php

@@ -65,11 +65,15 @@ final class FormBindingApplicatorIntegrationTest extends TestCase
         // RefreshDatabase wraps every PHPUnit test in a transaction; the
         // guard is exercised via the listener path (ApplyBindingsOnFormSubmit)
         // which opens its own transaction explicitly. Verify the guard
-        // exists in the source.
+        // exists in the source by checking for the throw of
+        // FormBindingInfraException (per RFC-WS-6 §Q3 v1.3 addition 2 — the
+        // 'no_transaction' developer-error maps onto temporary_error so the
+        // GlitchTip alert + retry-after workflow fires).
         $reflection = new \ReflectionClass(FormBindingApplicator::class);
         $source = file_get_contents($reflection->getFileName());
-        $this->assertStringContainsString('no_transaction', $source);
+        $this->assertStringContainsString('FormBindingInfraException', $source);
         $this->assertStringContainsString('DB::transactionLevel()', $source);
+        $this->assertStringContainsString('must be invoked inside DB::transaction', $source);
     }
 
     private function applicator(): FormBindingApplicator
@@ -151,7 +155,7 @@ final class FormBindingApplicatorIntegrationTest extends TestCase
 
     private function writeValue(string $submissionId, string $fieldId, mixed $value): void
     {
-        $row = new FormValue();
+        $row = new FormValue;
         $row->form_submission_id = $submissionId;
         $row->form_field_id = $fieldId;
         $row->setAttribute('value', $value);