OCO-Server MDM endpoint accepts self-signed enrollment signatures

OCO-Server is a self-hosted endpoint management application for computer inventory, software deployment, and mobile device management. Prior to 1.2.3,the Apple MDM enrollment endpoint `frontend/api-mdm.php` verifies the signed enrollment-request plist with `openssl_pkcs7_verify(..., PKCS7_NOVERIFY, ...)`. `PKCS7_NOVERIFY` disables signer certificate chain and trust validation, so the signature only has to be self-consistent with whatever certificate is embedded in the PKCS#7 blob. A self-signed certificate from an unrelated attacker is accepted. Because the endpoint trusts the `SERIAL` field taken from the unverified payload, anyone who knows a registered device's serial number can sign a forged plist (`SERIAL` = victim device, attacker-chosen `UDID`) with an arbitrary self-signed certificate; POST it unauthenticated to `/api-mdm.php/profile` (Content-Type: `application/pkcs7-signature`); and receive the victim device's freshly minted MDM identity: a certificate with `CN=<serial>` issued by the server's internal MDM device CA, bundled with its private key in a PKCS#12 payload inside the returned `.mobileconfig` enrollment profile. Additionally, the victim's `mobile_device` database row is silently overwritten with the attacker-supplied `UDID` (device-record hijack). With the stolen certificate and key, the attacker can impersonate the victim device on all subsequent MDM traffic (`/checkin`, `/mdm`, `/parameters`), which authenticate callers by the certificate CN (the serial number) via `checkSignature()` in the same file. This yields control over the victim device's MDM relationship: reading its management data, replacing its push token, and disrupting or redirecting its enrollment. Version 1.2.3 fixes the issue.