Compose multi-predicate detectors (AND / NOT / temporal window) #21

Detectors are single-predicate today. Adding boolean/temporal composition (require co-occurring conditions, negation, or a time window) would let detectors express real incident signatures.

Scope

• Extend the detector model + compiler + engine in v4/packages/kubeintellect-server/app/detectors/.
• Tests.

A meaty, well-scoped design + code task. Worth an RFC if the model changes significantly.