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/Relationship.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Attributes\Fillable;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+/**
+ * Social edge between two characters (friend, spouse, parent-child).
+ *
+ * For parent_child links character_a is the child and character_b is the parent.
+ */
+#[Fillable(['character_a_id', 'character_b_id', 'type', 'status'])]
+class Relationship extends Model
+{
+    public const TYPE_FRIEND = 'friend';
+
+    public const TYPE_SPOUSE = 'spouse';
+
+    public const TYPE_PARENT_CHILD = 'parent_child';
+
+    public const STATUS_PENDING = 'pending';
+
+    public const STATUS_ACCEPTED = 'accepted';
+
+    /**
+     * First character participant.
+     *
+     * @return BelongsTo<Character, $this>
+     */
+    public function characterA(): BelongsTo
+    {
+        return $this->belongsTo(Character::class, 'character_a_id');
+    }
+
+    /**
+     * Second character participant.
+     *
+     * @return BelongsTo<Character, $this>
+     */
+    public function characterB(): BelongsTo
+    {
+        return $this->belongsTo(Character::class, 'character_b_id');
+    }
+}