agent-platform release v4.15.3

The muster release detects and corrects drift (#287). The muster HelmRelease carries spec.driftDetection.mode: enabled (components.muster.driftDetection), the second release to carry it after kagent: on every reconcile — gitops.interval — helm-controller compares the release manifest with the cluster and re-applies what differs or is missing, as a server-side apply without a Helm revision. On a management cluster that came through the agentic-platform → agent-platform rename the live CiliumNetworkPolicy muster kept the old namespace in its egress selectors while the release manifest named the new one; Helm’s three-way merge patches only what changed between two release manifests, so the object stayed drifted across every upgrade and muster’s egress to Valkey stayed denied. No ignore rule: nothing of the platform edits this release’s objects in place. An installation that sets muster.autoscaling.enabled: true must add one for /spec/replicas on the Deployment (UPGRADE.md). tests/verify-kagent-wiring.py asserts the set of releases that carry drift detection; the ATS smoke edits an object of the muster release and sees it reverted.