feat(form-builder): form_field_validation_rules table + polymorphic owner + scope + cascade

api/app/Models/FormBuilder/FormFieldValidationRule.php

@@ -0,0 +1,55 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models\FormBuilder;
+
+use App\Enums\FormBuilder\FormFieldValidationRuleType;
+use App\Models\Scopes\FormFieldValidationRuleScope;
+use Illuminate\Database\Eloquent\Concerns\HasUlids;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+
+/**
+ * Relational home for what was `form_fields.validation_rules` and
+ * `form_field_library.validation_rules` JSON. Polymorphic owner — morph
+ * aliases `form_field` and `form_field_library`. See ARCH-FORM-BUILDER
+ * §17.4 and ARCH-CONSOLIDATION-ADDENDUM-2026-04-24 §Q3.
+ *
+ * One row per (owner, rule_type). `parameters` JSON holds the rule-type-
+ * specific configuration (e.g. `{ "value": 3 }` for `min_length`, or
+ * `{ "mime_types": [...] }` for `allowed_mime_types`). Parameter shape
+ * validation lives in `FormFieldValidationRuleService`, not on the model.
+ */
+final class FormFieldValidationRule extends Model
+{
+    use HasFactory;
+    use HasUlids;
+
+    protected $table = 'form_field_validation_rules';
+
+    protected static function booted(): void
+    {
+        static::addGlobalScope(new FormFieldValidationRuleScope());
+    }
+
+    protected $fillable = [
+        'owner_type',
+        'owner_id',
+        'rule_type',
+        'parameters',
+        'error_message_key',
+    ];
+
+    /** @var array<string, string> */
+    protected $casts = [
+        'rule_type' => FormFieldValidationRuleType::class,
+        'parameters' => 'array',
+    ];
+
+    public function owner(): MorphTo
+    {
+        return $this->morphTo('owner', 'owner_type', 'owner_id');
+    }
+}