feat(media): add public URL generation for media files and improve S3 integration

Introduce `getPublicUrl` in `S3Service` for generating public URLs. Replace custom file URL generation logic across services with the new method. Add media controller for file streaming and update related tests. Adjust frontend to display user roles instead of email in the sidebar. Update environment schema to include optional `API_URL`. Fix help page contact email.

frontend/src/app/(dashboard)/help/page.tsx

@@ -63,7 +63,7 @@ export default function HelpPage() {
 				<p className="text-muted-foreground">
 					N'hésitez pas à nous contacter sur nos réseaux sociaux ou par email.
 				</p>
-				<p className="font-semibold text-primary">contact@memegoat.local</p>
+				<p className="font-semibold text-primary">contact@memegoat.fr</p>
 			</div>
 		</div>
 	);