Refactor invoice PDF generation and VAT validation

- Updated PDF template to display a fixed software code instead of "SOFTWARE".
- Changed VAT label to include tax label dynamically and set to 0% for certain conditions.
- Enhanced JavaScript for VAT number validation with asynchronous checks against the VIES database.
- Implemented debounce for VAT number input to optimize validation calls.
- Updated country settings to include country codes for VAT validation.
- Modified email sending functions in webhook handlers to use dynamic attachment names for invoices.

api/v2/post/vat_check.php

@@ -0,0 +1,86 @@
+<?php
+defined($security_key) or exit;
+
+//------------------------------------------
+// VAT Number Validation (VIES Proxy)
+//------------------------------------------
+
+// CONTENT FROM API (POST)
+$post_content = json_decode($input, true);
+
+// Validate input
+if (empty($post_content['countryCode']) || empty($post_content['vatNumber'])) {
+    http_response_code(400);
+    echo json_encode([
+        'error' => 'Missing required parameters: countryCode and vatNumber'
+    ]);
+    exit;
+}
+
+$countryCode = strtoupper(trim($post_content['countryCode']));
+$vatNumber = $post_content['vatNumber'];
+
+// Remove all whitespace from VAT number
+$vatNumber = preg_replace('/\s+/', '', $vatNumber);
+
+// Remove country code prefix if included in VAT number
+if (strpos($vatNumber, $countryCode) === 0) {
+    $vatNumber = substr($vatNumber, strlen($countryCode));
+}
+
+// VIES API endpoint
+$viesUrl = 'https://ec.europa.eu/taxation_customs/vies/rest-api/check-vat-number';
+
+// Prepare request data
+$requestData = json_encode([
+    'countryCode' => $countryCode,
+    'vatNumber' => $vatNumber
+]);
+
+// Initialize cURL
+$ch = curl_init($viesUrl);
+curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
+curl_setopt($ch, CURLOPT_POST, true);
+curl_setopt($ch, CURLOPT_POSTFIELDS, $requestData);
+curl_setopt($ch, CURLOPT_HTTPHEADER, [
+    'Content-Type: application/json',
+    'Accept: application/json'
+]);
+curl_setopt($ch, CURLOPT_TIMEOUT, 10); // 10 second timeout
+
+// Execute request
+$response = curl_exec($ch);
+$httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
+$curlError = curl_error($ch);
+curl_close($ch);
+
+// Check for cURL errors
+if ($curlError) {
+    http_response_code(500);
+    echo json_encode([
+        'error' => 'Failed to connect to VIES service',
+        'details' => $curlError
+    ]);
+    exit;
+}
+
+// Parse VIES response regardless of HTTP code
+$viesData = json_decode($response, true);
+
+// If we can't parse JSON, return an error
+if (json_last_error() !== JSON_ERROR_NONE) {
+    http_response_code(500);
+    echo json_encode([
+        'error' => 'Invalid response from VIES service',
+        'httpCode' => $httpCode,
+        'response' => $response
+    ]);
+    exit;
+}
+
+// Always return 200 OK to the client with the VIES data
+// The client will check the 'valid' field in the response
+http_response_code(200);
+echo json_encode($viesData);
+
+?>