feat: save ai usage

app/Models/AiUsage.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace App\Models;
+
+use App\Enums\AiUsageStatus;
+use App\Enums\AiUsageType;
+use Illuminate\Database\Eloquent\Concerns\HasUlids;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+
+class AiUsage extends Model
+{
+    /** @use HasFactory<\Database\Factories\AiUsageFactory> */
+    use HasFactory, HasUlids;
+
+    protected $fillable = [
+        'user_id',
+        'type',
+        'status',
+        'input',
+        'output',
+        'provider',
+        'model',
+        'prompt_tokens',
+        'completion_tokens',
+        'total_tokens',
+        'error_message',
+        'related_type',
+        'related_id',
+    ];
+
+    public function user(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    public function related(): MorphTo
+    {
+        return $this->morphTo();
+    }
+
+    protected function casts(): array
+    {
+        return [
+            'type' => AiUsageType::class,
+            'status' => AiUsageStatus::class,
+            'input' => 'array',
+            'output' => 'array',
+            'prompt_tokens' => 'integer',
+            'completion_tokens' => 'integer',
+            'total_tokens' => 'integer',
+        ];
+    }
+}