feat(form-field): add form_field_options table, service, scope, cascade

Fourth and final WS-5 sibling. Polymorphic morph-owned table for the
RADIO / SELECT / MULTISELECT / CHECKBOX_LIST option rows, shared
between form_fields and form_field_library via the owner_type
discriminator. Matches the WS-5a (bindings) / WS-5b (validation_rules
+ configs) pattern one-for-one: dedicated service as single writer,
UNION-over-two-owner-chains scope, shared cascade observer.

Row shape:
  - value         canonical storage value (string ≤255, UNIQUE per owner)
  - label         default-locale display label (string ≤255)
  - sort_order    int unsigned
  - translations  JSON { "<locale>": "<translated label>" }

The UNIQUE(owner_type, owner_id, value) index ffo_owner_value_unique
is the seed-bug guard — duplicate values per field have no semantic
meaning and must fail at both the service layer (assertSpecsValid)
and the DB level.

Activity log: field.options_replaced emits on FormField subject only,
per the §6.7 WS-5a / §17.4.2 WS-5b convention that library-level
changes are silent in activity log.

No production reads yet. The form_fields.options and
form_field_library.options JSON columns remain the active source of
truth until the commit-3 reader switch — accessing $field->options
still resolves through the JSON cast in commit 1, so model tests
exercise the new morphMany via $field->options() (explicit relation
call). Both FormField and FormFieldLibrary now carry an `options`
morphMany alongside `bindings`, `validation_rules`, and `configs`.

Cascade: FormFieldChildTablesCascadeObserver gains form_field_options
as the fourth child cleaned on owner delete (both FormField soft/
force-delete and FormFieldLibrary delete).

Migration step-count tests in WS-5a/b/c bumped by 1 to account for
the new create_form_field_options_table on the migration stack.

Base scope-class extraction across the four siblings — deliberately
deferred to a follow-up work package per addendum §17.4.3 / §17.5.3.
Now that all four concrete implementations exist, the "what actually
varies" question can be answered empirically.

Tests: 1158 → 1182 green (+24 tests / +42 assertions).

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

api/app/Observers/FormBuilder/FormFieldChildTablesCascadeObserver.php

@@ -20,6 +20,7 @@ use Illuminate\Support\Facades\Schema;
  *                                                  per addendum Q3: library
  *                                                  is explicitly out of
  *                                                  scope for conditional_logic)
+ *   - `form_field_options`                        (WS-5d — both owner types)
  *
  * The conditions sibling table cascades automatically via the `group_id`
  * FK on the groups table — no direct entry here.
@@ -59,6 +60,13 @@ final class FormFieldChildTablesCascadeObserver
                 ->delete();
         }
 
+        if (Schema::hasTable('form_field_options')) {
+            DB::table('form_field_options')
+                ->where('owner_type', $ownerType)
+                ->where('owner_id', $ownerId)
+                ->delete();
+        }
+
         // Conditional-logic groups only apply to FormField (addendum Q3:
         // library mirror is out of scope). Condition rows cascade via
         // the group_id FK on the conditions table.