fix: handle axios errors in Turnstile service to prevent misleading 500 responses

Unhandled axios errors from Cloudflare API were propagating as 500 Internal Server Error
with confusing message "Request failed with status code 400". Now catches these errors
and returns a proper 400 BadRequest with a clear message.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: gugu

backend/src/shared/services/turnstile.service.ts

@@ -29,15 +29,21 @@ export class TurnstileService {
 		formData.append('secret', secretKey);
 		formData.append('response', token);
 
-		const response = await axios.post<TurnstileVerifyResponse>(this.verifyUrl, formData.toString(), {
-			headers: {
-				'Content-Type': 'application/x-www-form-urlencoded',
-			},
-		});
-
-		if (!response.data.success) {
-			const errorCodes = response.data['error-codes']?.join(', ') || 'Unknown error';
-			throw new BadRequestException(`Turnstile verification failed: ${errorCodes}`);
+		try {
+			const response = await axios.post<TurnstileVerifyResponse>(this.verifyUrl, formData.toString(), {
+				headers: {
+					'Content-Type': 'application/x-www-form-urlencoded',
+				},
+			});
+
+			if (!response.data.success) {
+				const errorCodes = response.data['error-codes']?.join(', ') || 'Unknown error';
+				throw new BadRequestException(`Turnstile verification failed: ${errorCodes}`);
+			}
+		} catch (error) {
+			if (error instanceof BadRequestException) throw error;
+			console.error('Turnstile verification error:', error?.response?.data || error?.message || error);
+			throw new BadRequestException('Turnstile verification failed. Please try again.');
 		}
 
 		return true;