feat: implement AI styling foundation and billing scope rework

app/Models/AiUsageLedger.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class AiUsageLedger extends Model
+{
+    use HasFactory;
+
+    public const TYPE_DEBIT = 'debit';
+
+    public const TYPE_CREDIT = 'credit';
+
+    public const TYPE_REFUND = 'refund';
+
+    public const TYPE_ADJUSTMENT = 'adjustment';
+
+    protected $fillable = [
+        'tenant_id',
+        'event_id',
+        'request_id',
+        'entry_type',
+        'quantity',
+        'unit_cost_usd',
+        'amount_usd',
+        'currency',
+        'package_context',
+        'notes',
+        'recorded_at',
+        'metadata',
+    ];
+
+    protected function casts(): array
+    {
+        return [
+            'unit_cost_usd' => 'decimal:5',
+            'amount_usd' => 'decimal:5',
+            'recorded_at' => 'datetime',
+            'metadata' => 'array',
+        ];
+    }
+
+    public function tenant(): BelongsTo
+    {
+        return $this->belongsTo(Tenant::class);
+    }
+
+    public function event(): BelongsTo
+    {
+        return $this->belongsTo(Event::class);
+    }
+
+    public function request(): BelongsTo
+    {
+        return $this->belongsTo(AiEditRequest::class, 'request_id');
+    }
+}