🗓️ Add MeetupEventFactory, implement rate limiting for calendar downloads, and enhance test coverage

- **Added:** `MeetupEventFactory` for generating test data.
- **Implemented:** Rate limiting (`throttle:calendar`) for `stream-calendar` routes to prevent abuse.
- **Enhanced:** `DownloadMeetupCalendar` controller with validation and cleaner query structure.
- **Added:** Feature tests for calendar downloading, invalid input handling, and rate limiting.

database/factories/MeetupEventFactory.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace Database\Factories;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends \Illuminate\Database\Eloquent\Factories\Factory<\App\Models\MeetupEvent>
+ */
+class MeetupEventFactory extends Factory
+{
+    /**
+     * Define the model's default state.
+     *
+     * @return array<string, mixed>
+     */
+    public function definition(): array
+    {
+        return [
+            'meetup_id' => \App\Models\Meetup::factory(),
+            'start' => now()->addWeek(),
+            'location' => fake()->address(),
+            'description' => fake()->paragraph(),
+            'link' => fake()->url(),
+            'attendees' => [],
+            'might_attendees' => [],
+            'created_by' => \App\Models\User::factory(),
+        ];
+    }
+}