feat(form-builder): form_field_conditional_logic_{groups,conditions} tables + OrganisationScope cap raise to 5

WS-5c commit 1 of 4 — relational infrastructure for the conditional-
logic tree that replaces form_fields.conditional_logic JSON (ARCH-
FORM-BUILDER §8; addendum Q3 WS-5c).

Tables: groups (nesting via parent_group_id) + conditions (leaves,
value JSON nullable for empty/not_empty). Simple FK to form_fields —
addendum Q3 explicitly excludes form_field_library from conditional_
logic scope, so no polymorphic morph here.

OrganisationScope cap raised 3 → 5 hops. The conditions chain is
4 hops (condition → group → field → schema → organisation_id column)
and the new cap gives headroom for future deeper trees without
denormalising form_field_id onto conditions.

Cascade observer (FormFieldChildTablesCascadeObserver) extended to
physically delete the new groups table on FormField delete (hard or
soft). Conditions cascade automatically via the group_id FK on the
groups table.

Factories: FormFieldConditionalLogicGroupFactory, FormFieldConditional
LogicConditionFactory, and FormFieldFactory::withConditionalLogic($tree)
for concise test fixtures.

Tests: 16 new under tests/Feature/FormBuilder/ConditionalLogic/
(relation, scope, cascade, enum catalogue). 3 new scope-cap tests in
ScopeLeakageTest verify 4/5-hop chains pass and 6-hop throws. Hardcoded
rollback step counts in WS-5a/b migration tests bumped for the 2 new
WS-5c migrations. Baseline 1104 → 1122 green (2988 → 3032 assertions).

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

api/app/Models/FormBuilder/FormField.php

@@ -119,6 +119,23 @@ final class FormField extends Model
         return $this->morphMany(FormFieldConfig::class, 'owner');
     }
 
+    public function conditionalLogicGroups(): HasMany
+    {
+        return $this->hasMany(FormFieldConditionalLogicGroup::class, 'form_field_id');
+    }
+
+    /**
+     * The tree root: the group with `parent_group_id IS NULL`. Fields
+     * without any conditional logic return null. Only one root is
+     * supported per field — enforced by the service layer's `replaceLogic`.
+     */
+    public function rootConditionalLogicGroup(): ?FormFieldConditionalLogicGroup
+    {
+        return $this->conditionalLogicGroups()
+            ->whereNull('parent_group_id')
+            ->first();
+    }
+
     /**
      * Nuanced activity log (ARCH §17.1; S1 Phase 4b). Callers choose which
      * events are worth logging — e.g. created/deleted/restored, field_type