feat: add system configuration (A-03) — map center, zoom, radius min/max

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Models/Setting.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Support\Facades\Cache;
+
+class Setting extends Model
+{
+    protected $fillable = ['key', 'value', 'label'];
+
+    public static function getAll(): array
+    {
+        return Cache::remember('app_settings', 300, function () {
+            return static::pluck('value', 'key')->toArray();
+        });
+    }
+
+    public static function get(string $key, mixed $default = null): mixed
+    {
+        return static::getAll()[$key] ?? $default;
+    }
+
+    public static function set(string $key, string $value): void
+    {
+        static::where('key', $key)->update(['value' => $value]);
+        Cache::forget('app_settings');
+    }
+}