feat: validate email via Emailable, remove auto-download, fix keyboard nav in inputs

- Plug Emailable API into checkEmailDeliverability (fail open if no key)
- Show inline red error + shake animation on email field when address is undeliverable
- Remove window.open auto-download after form submission; success now checks result.success
- Disable arrow-key slide navigation when an input or textarea is focused

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

site/config/routes/download-white-paper.php

@@ -49,10 +49,43 @@ function parseContact(array $body): array
     return compact('firstName', 'lastName', 'email', 'company', 'role');
 }
 
-function checkEmailDeliverability(string $email): bool
+function checkEmailDeliverability(string $email, string $apiKey): bool
 {
-    // Plug in an external email validation API here (e.g. Hunter, ZeroBounce, AbstractAPI)
-    return true;
+    if ($apiKey === '') {
+        error_log('[WP] Emailable: no api_key configured, skipping email check');
+        return true;
+    }
+
+    $url = 'https://api.emailable.com/v1/verify?' . http_build_query([
+        'email'   => $email,
+        'api_key' => $apiKey,
+    ]);
+
+    $ch = curl_init();
+    curl_setopt_array($ch, [
+        CURLOPT_URL            => $url,
+        CURLOPT_RETURNTRANSFER => true,
+        CURLOPT_HTTPGET        => true,
+        CURLOPT_TIMEOUT        => 8,
+        CURLOPT_SSL_VERIFYPEER => true,
+    ]);
+
+    $response  = curl_exec($ch);
+    $httpCode  = curl_getinfo($ch, CURLINFO_HTTP_CODE);
+    $curlError = curl_error($ch);
+    curl_close($ch);
+
+    if ($response === false || $httpCode !== 200) {
+        error_log('[WP] Emailable check failed (HTTP ' . $httpCode . '): ' . $curlError);
+        return true; // fail open
+    }
+
+    $data  = json_decode($response, true);
+    $state = $data['state'] ?? 'unknown';
+
+    error_log('[WP] Emailable response for ' . $email . ': state=' . $state . ' | raw=' . $response);
+
+    return $state !== 'undeliverable';
 }
 
 function upsertKirbyContact(\Kirby\Cms\Page $page, array $contact): void
@@ -179,7 +212,8 @@ return [
 
         $contact = parseContact($body);
 
-        if (!checkEmailDeliverability($contact['email'])) {
+        $emailableApiKey = kirby()->option('emailable_whitepaper', [])['api_key'] ?? '';
+        if (!checkEmailDeliverability($contact['email'], $emailableApiKey)) {
             wpReject(422, 'Undeliverable email');
         }