Fix #4-#8: mail virtual domains, DNS verified, reseller isolation, missing DB tables

#4: Postfix virtual mailbox config (virtual_mailbox_domains/maps, vmail user, maildir
    at /var/mail/vhosts/%d/%n). Dovecot SQL backend pointed at novacpx.email_accounts
    with SHA512-CRYPT passdb and per-domain Maildir userdb.

#5: BIND9 confirmed working — dig @localhost resolves testdomain1.com correctly.

#6: Certbot 2.9.0 confirmed installed; domains.document_root wired; infrastructure
    ready for live domain issuance (testdomain1.com not publicly resolvable so
    dry-run expected to fail).

#7: Fixed all broken user-panel API queries — missing tables (databases, ftp_accounts,
    ssl_certs, cron_jobs, php_configs, notifications) created; `databases` reserved-word
    backtick-quoted across DatabaseManager+endpoints; domains.php is_primary→type=main,
    doc_root→document_root column fixes; DNSManager::createZone call signature fixed;
    stats/account auto-resolves account_id for user role.

#8: assert_account_access() helper added to api/index.php; reseller ownership check
    wired into email, ftp, databases, domains, dns, ssl endpoints.

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

panel/api/endpoints/dns.php

@@ -12,6 +12,7 @@ if ($user['role'] === 'user') {
     $accountId = $acct ? (int)$acct['id'] : null;
 } else {
     $accountId = (int)($_GET['account_id'] ?? $body['account_id'] ?? 0) ?: null;
+    if ($accountId && $user['role'] === 'reseller') assert_account_access($accountId);
 }
 
 match ($action) {