feat(monitors): heartbeat token, ping recording and overdue verdict

server/internal/models/monitor.go

@@ -92,6 +92,8 @@ type Monitor struct {
 	// HeartbeatTokenHash is the SHA-256 of the ping token. The token itself is
 	// shown once, on create or rotate, and never stored.
 	HeartbeatTokenHash string `bson:"heartbeat_token_hash,omitempty" json:"-"`
+	// HeartbeatToken is the plaintext token, set only on the create response.
+	HeartbeatToken string `bson:"-" json:"heartbeat_token,omitempty"`
 }
 
 type Incident struct {