feat: Add FaceAI integration with handoff and return functionality

- Introduced a new workspace for FaceAI in package.json.
- Implemented FaceAI handoff logic in faceai_handoff.php, including identity verification and token signing.
- Created faceai_return.php to handle return requests from FaceAI, validating tokens and forwarding results.
- Developed faceai_simulator.php and faceai_simulator_view.php for simulating the FaceAI interface with demo photos.
- Enhanced rus-ecom-240621.js to support new FaceAI features, including dynamic URL building and button integration.
- Added faceai_config.php for configuration management, including environment variable handling and utility functions.
- Updated HTML structure and styles in simulator view for better user experience.

www/faceai_return.php

@@ -0,0 +1,56 @@
+<?php
+
+require_once __DIR__ . '/faceai_config.php';
+require_once __DIR__ . '/faceai_simulator_view.php';
+
+$config = faceai_config();
+
+try {
+    $resultId = faceai_request_value('resultId');
+    $token = faceai_request_value('token');
+
+    if ($resultId === '' || $token === '') {
+        faceai_render_message_page(
+            'FaceAI return non disponibile',
+            'Mancano resultId o token nella chiamata di ritorno da FaceAI.',
+            array(),
+            400
+        );
+    }
+
+    $payload = faceai_verify_payload($token, $config['shared_secret']);
+    if (($payload['type'] ?? '') !== 'return') {
+        throw new RuntimeException('Wrong return token type.');
+    }
+
+    if ((string) ($payload['resultId'] ?? '') !== $resultId) {
+        throw new RuntimeException('Result id mismatch.');
+    }
+
+    if ($config['return_forward_url'] !== '') {
+        header('Location: ' . faceai_build_url($config['return_forward_url'], array(
+            'resultId' => $resultId,
+            'token' => $token
+        )), true, 302);
+        exit;
+    }
+
+    $bridgeUrl = faceai_build_url($config['backend_internal_url'] . '/bridge/results/' . rawurlencode($resultId), array(
+        'token' => $token
+    ));
+    $result = faceai_fetch_json($bridgeUrl);
+
+    faceai_sim_render_page(array(
+        'raceId' => (string) ($result['raceId'] ?? ($payload['raceId'] ?? '')),
+        'lang' => (string) ($result['lang'] ?? 'it'),
+        'raceSlug' => (string) ($result['raceId'] ?? ($payload['raceId'] ?? '')), 
+        'raceName' => (string) ($result['raceName'] ?? ('Race ' . ($payload['raceId'] ?? ''))),
+        'returnUrl' => (string) ($result['returnUrl'] ?? 'faceai_simulator.php'),
+        'banner' => 'Vista filtrata da FaceAI. Sono state trovate <strong>' . count($result['matches'] ?? array()) . '</strong> foto corrispondenti per l utente corrente.',
+        'totalLabel' => count($result['matches'] ?? array()) . ' foto da FaceAI',
+        'photos' => is_array($result['matches'] ?? null) ? $result['matches'] : array(),
+        'showSimulatorBootstrap' => false
+    ));
+} catch (Throwable $error) {
+    faceai_render_message_page('Errore return FaceAI', $error->getMessage(), array(), 500);
+}