CVE-2026-53521: Nezha Monitoring: Stored future DDNS profile ID allows unauthorized use of another user's DDNS profile context

PATCH /server/{id} accepts and persists nonexistent ddns_profiles IDs for a member-owned server. If another user later creates a DDNS profile with one of those IDs, the DDNS worker resolves the stored ID and dispatches an update using the other user’s DDNS profile configuration in the context of the attacker’s server.

This is a second-order authorization bypass: direct binding to an existing foreign DDNS profile is correctly denied, but an unresolved future ID can be stored first and later becomes a live cross-user reference.

The behavior was validated locally with focused regression tests.