feat: product pricing plans

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

app/Models/PricingPlan.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class PricingPlan extends Model
+{
+    public const PERIODS = ['monthly', 'yearly', 'one-time'];
+
+    protected $fillable = ['product_id', 'name', 'price', 'period', 'description', 'position'];
+
+    protected function casts(): array
+    {
+        return ['price' => 'decimal:2'];
+    }
+
+    public function product(): BelongsTo
+    {
+        return $this->belongsTo(Product::class);
+    }
+
+    /**
+     * Price formatted for display, e.g. "€9.99" ("€0" for free plans).
+     */
+    public function formattedPrice(): string
+    {
+        return (float) $this->price == 0 ? '€0' : '€'.number_format((float) $this->price, 2);
+    }
+}