🏆 Add highscore feature with API endpoints, validations, and tests

- **Added:** Endpoints for submitting highscores (`highscores.store`) and retrieving the leaderboard (`highscores.index`).
- **Implemented:** Validation rules via `StoreHighscoreRequest` to ensure highscore integrity.
- **Included:** `Highscore` model, migration, and factory for data handling and seeding.
- **Enhanced:** Comprehensive feature tests covering submission, updating, retrieval, and payload validation.

database/factories/HighscoreFactory.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Database\Factories;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends \Illuminate\Database\Eloquent\Factories\Factory<\App\Models\Highscore>
+ */
+class HighscoreFactory extends Factory
+{
+    /**
+     * Define the model's default state.
+     *
+     * @return array<string, mixed>
+     */
+    public function definition(): array
+    {
+        return [
+            'npub' => 'npub1'.fake()->regexify('[a-z0-9]{20}'),
+            'name' => fake()->name(),
+            'satoshis' => fake()->numberBetween(0, 100000),
+            'blocks' => fake()->numberBetween(0, 1000),
+            'achieved_at' => fake()->dateTimeBetween('-1 year', 'now'),
+        ];
+    }
+}