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/accounts.php

@@ -37,7 +37,7 @@ match ($action) {
                     p.name as package_name,
                     (SELECT COUNT(*) FROM domains WHERE account_id = a.id) as domain_count,
                     (SELECT COUNT(*) FROM email_accounts WHERE account_id = a.id) as email_count,
-                    (SELECT COUNT(*) FROM databases WHERE account_id = a.id) as db_count
+                    (SELECT COUNT(*) FROM `databases` WHERE account_id = a.id) as db_count
              FROM accounts a
              JOIN users u ON u.id = a.user_id
              LEFT JOIN packages p ON p.id = a.package_id
@@ -132,7 +132,7 @@ match ($action) {
             'disk_limit_mb'  => $pkg['disk_mb'] ?? 0,
             'email_count'    => $db->fetchOne("SELECT COUNT(*) c FROM email_accounts WHERE account_id = ?", [$id])['c'],
             'email_limit'    => $pkg['max_email'] ?? 0,
-            'db_count'       => $db->fetchOne("SELECT COUNT(*) c FROM databases WHERE account_id = ?", [$id])['c'],
+            'db_count'       => $db->fetchOne("SELECT COUNT(*) c FROM `databases` WHERE account_id = ?", [$id])['c'],
             'db_limit'       => $pkg['max_databases'] ?? 0,
             'domain_count'   => $db->fetchOne("SELECT COUNT(*) c FROM domains WHERE account_id = ?", [$id])['c'],
             'domain_limit'   => $pkg['max_domains'] ?? 0,