Add webhook to auto-deploy watchgether-web

watchgether-web has no PHP runtime of its own (static files served by
a plain nginx container), so it reuses this repo's PHP/nginx to receive
its Gitea webhook and git-pull the separate watchgether-web checkout.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -1,2 +1,3 @@
 config/database.php
 webhook.log
+webhook-web.log

webhook-web.php

@@ -0,0 +1,32 @@
+<?php
+// webhook-web.php
+// Déclenché par le webhook Gitea du dépôt watchgether-web (séparé de l'API).
+// Vit ici parce que c'est le seul endroit du serveur avec un runtime PHP ;
+// le front est servi par un simple conteneur nginx statique sans exécution possible.
+
+require_once __DIR__ . '/config/database.php';
+
+if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
+    http_response_code(405);
+    exit('Method not allowed');
+}
+
+$database = new Database();
+$secret = $database->webhook_secret;
+
+$payload = file_get_contents('php://input');
+$signatureHeader = $_SERVER['HTTP_X_GITEA_SIGNATURE'] ?? '';
+$expectedSignature = hash_hmac('sha256', $payload, $secret);
+
+if (!$signatureHeader || !hash_equals($expectedSignature, $signatureHeader)) {
+    http_response_code(403);
+    file_put_contents(__DIR__ . '/webhook-web.log', date('Y-m-d H:i:s') . " - Tentative refusée (signature invalide)\n", FILE_APPEND);
+    exit('Forbidden');
+}
+
+$webSiteDir = '/home/admin2root/watchgether-web/site';
+$output = shell_exec("cd {$webSiteDir} && git fetch origin && git reset --hard origin/main 2>&1");
+
+file_put_contents(__DIR__ . '/webhook-web.log', date('Y-m-d H:i:s') . "\n" . $output . "\n---\n", FILE_APPEND);
+
+echo "Web sync done.";