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/CharacterMessage.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Attributes\Fillable;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+/**
+ * Chat message exchanged between two characters.
+ */
+#[Fillable(['from_character_id', 'to_character_id', 'body'])]
+class CharacterMessage extends Model
+{
+    /**
+     * Sending character.
+     *
+     * @return BelongsTo<Character, $this>
+     */
+    public function fromCharacter(): BelongsTo
+    {
+        return $this->belongsTo(Character::class, 'from_character_id');
+    }
+
+    /**
+     * Receiving character.
+     *
+     * @return BelongsTo<Character, $this>
+     */
+    public function toCharacter(): BelongsTo
+    {
+        return $this->belongsTo(Character::class, 'to_character_id');
+    }
+}