Add full API endpoint suite, lib managers, webmail (Roundcube :8883), and NovaCPX icon/branding assets

- 14 API endpoints: accounts, packages, domains, dns, email, databases, ftp, ssl, cron, php, files, stats, webmail, server_setup
- 8 lib managers: AccountManager, VhostManager, DNSManager, EmailManager, DatabaseManager, PHPManager, FTPManager, SSLManager
- Roundcube webmail on dedicated port 8883 (sequenced after 8880/8881/8882)
- Custom NovaCPX SVG icon sprite (30+ unique icons), logo, mark, favicon
- PORT_WEBMAIL=8883 wired into Core.php, install.sh, UFW, Fail2Ban, credentials file

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

panel/api/endpoints/webmail.php

@@ -0,0 +1,53 @@
+<?php
+/**
+ * Webmail endpoint — Roundcube integration proxy
+ * Redirects authenticated users to Roundcube with SSO token
+ */
+$db   = DB::getInstance();
+$body = json_decode(file_get_contents('php://input'), true) ?? [];
+
+$user = Auth::getInstance()->user();
+
+match ($action) {
+    'url' => (function() use ($db, $body, $user) {
+        $accountId = $user['role'] === 'user'
+            ? (int)($db->fetchOne("SELECT id FROM accounts WHERE user_id = ?", [$user['uid']])['id'] ?? 0)
+            : (int)($body['account_id'] ?? 0);
+        $acct = $db->fetchOne("SELECT * FROM accounts WHERE id = ?", [$accountId]);
+        if (!$acct) Response::error("Account not found");
+
+        $domain = $acct['domain'];
+        // Roundcube installed by default at /var/www/roundcube
+        $rcUrl  = "https://{$domain}/webmail/";
+        // Check if Roundcube is installed
+        $installed = file_exists('/var/www/roundcube/index.php');
+        Response::success([
+            'url'       => $rcUrl,
+            'installed' => $installed,
+            'domain'    => $domain,
+        ]);
+    })(),
+
+    'install' => (function() use ($db) {
+        Auth::getInstance()->requireRole(['admin']);
+        // Background install
+        $logFile = '/var/log/novacpx/webmail-install.log';
+        $cmd = 'apt-get install -y roundcube roundcube-mysql php8.3-intl > ' . escapeshellarg($logFile) . ' 2>&1 && ' .
+               'ln -sf /usr/share/roundcube /var/www/roundcube >> ' . escapeshellarg($logFile) . ' 2>&1';
+        shell_exec("nohup bash -c " . escapeshellarg($cmd) . " &");
+        Response::success(['log' => $logFile], 'Webmail install started');
+    })(),
+
+    'login-url' => (function() use ($db, $body, $user) {
+        // Generate a short-lived token for auto-login
+        $emailAccount = $db->fetchOne("SELECT * FROM email_accounts WHERE id = ?", [(int)($body['email_id'] ?? 0)]);
+        if (!$emailAccount) Response::error("Email account not found");
+        $token = bin2hex(random_bytes(16));
+        $db->execute("INSERT INTO api_tokens (user_id, token, purpose, expires_at) VALUES (?,?,?,DATE_ADD(NOW(), INTERVAL 30 SECOND))",
+            [$user['uid'], hash('sha256', $token), 'webmail_sso']);
+        $domain  = parse_url($emailAccount['email'], PHP_URL_HOST) ?: '';
+        Response::success(['url' => "https://{$domain}/webmail/?_token={$token}"]);
+    })(),
+
+    default => Response::error("Unknown webmail action: $action", 404),
+};