🔥 Add initial database migrations, seeders, and factories

🎨 Refactor `Lecturer` model to include new fields and factory usage
🔧 Update `DatabaseSeeder` to handle default seeds
🛠️ Enhance `einundzwanzig` database configuration for SQLite compatibility

database/factories/CourseFactory.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace Database\Factories;
+
+use App\Models\Course;
+use App\Models\Lecturer;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends Factory<Course>
+ */
+class CourseFactory extends Factory
+{
+    /**
+     * @return array<string, mixed>
+     */
+    public function definition(): array
+    {
+        $titles = [
+            'Bitcoin Basics',
+            'Self Custody und Hardware Wallets',
+            'Lightning Network 101',
+            'Nostr Einführung',
+            'Bitcoin für Unternehmer',
+            'Privacy & Coinjoin',
+            'Running Your Own Node',
+        ];
+
+        return [
+            'lecturer_id' => Lecturer::factory(),
+            'name' => fake()->randomElement($titles),
+            'description' => fake()->paragraphs(2, true),
+            'duration_minutes' => fake()->randomElement([60, 90, 120, 180]),
+        ];
+    }
+
+    public function bitcoinBasics(): static
+    {
+        return $this->state(fn () => [
+            'name' => 'Bitcoin Basics',
+            'description' => 'Eine umfassende Einführung in Bitcoin: Was ist Bitcoin, wie funktioniert die Blockchain, warum ist es revolutionär. Perfekt für Einsteiger.',
+            'duration_minutes' => 90,
+        ]);
+    }
+}