feat: Add Discord alert webhook, ContactCategory enum, form request

- Added Discord alert webhook URL to .env.example
- Created ContactCategory enum with humanReadable method
- Implemented ContactSubmissionRequest form request
- Added ContactSubmission model with fillable and casts properties
- Included configurations for Discord alerts and honeypot protection

app/Http/Requests/ContactSubmissionRequest.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace App\Http\Requests;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class ContactSubmissionRequest extends FormRequest
+{
+    public function rules(): array
+    {
+        return [
+            'name'     => ['required', 'max:254'],
+            'email'    => ['required', 'email', 'max:254'],
+            'discord'  => ['nullable', 'min:2', 'max:34'],
+            'category' => ['required', 'in:question,advertising,bug_report,feedback,other'],
+            'subject'  => ['required', 'max:254'],
+            'message'  => ['required', 'unique:contact_submissions', 'max:3500'],
+        ];
+    }
+
+    public function authorize(): bool
+    {
+        return true;
+    }
+}