add SslCheckConfig protobuf message and executeSSLCheck function that connects via crypto/tls, reads the peer certificate expiry, and returns OK/WARNING/CRITICAL based on a configurable warning_days threshold.
Cover WebSocket session lifecycle (result channels, SNMP batch flushing, heartbeats, restart), MikroTik TLS TOFU verification mismatch, worker pool exhaustion, plaintext WebSocket rejection, HTTP/TCP/DNS check execution, IPv4 fallback, and customer network edge cases. Make heartbeat intervals and toWebSocketURL exit injectable for testing.
