feat(world): add persistent citizen simulation with needs, jobs, and social features

- Adds Character model with survival needs (hunger, thirst, energy) and state machine
- Implements city:tick world ticker for offline progression every minute
- Adds city territory expansion and building construction system
- Introduces job economy, inventory, and transaction audit trail
- Adds social graph (friends, marriage, children) and character chat
- Implements admin approval workflow for new registrations
- Adds hospital admission system for traffic accidents
- Includes comprehensive feature tests and world seeders

app/Models/Transaction.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Attributes\Fillable;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+/**
+ * Audit record of an economic exchange involving characters and/or stores.
+ */
+#[Fillable(['from_character_id', 'to_character_id', 'store_id', 'item', 'qty', 'amount'])]
+class Transaction extends Model
+{
+    /**
+     * Character that paid or gave items.
+     *
+     * @return BelongsTo<Character, $this>
+     */
+    public function fromCharacter(): BelongsTo
+    {
+        return $this->belongsTo(Character::class, 'from_character_id');
+    }
+
+    /**
+     * Character that received payment or items.
+     *
+     * @return BelongsTo<Character, $this>
+     */
+    public function toCharacter(): BelongsTo
+    {
+        return $this->belongsTo(Character::class, 'to_character_id');
+    }
+
+    /**
+     * Store involved in the exchange, when any.
+     *
+     * @return BelongsTo<Store, $this>
+     */
+    public function store(): BelongsTo
+    {
+        return $this->belongsTo(Store::class);
+    }
+
+    /**
+     * Get the attributes that should be cast.
+     *
+     * @return array<string, string>
+     */
+    protected function casts(): array
+    {
+        return [
+            'amount' => 'float',
+            'qty' => 'integer',
+        ];
+    }
+}