docs: narrow T4 operator ownership boundary

[iarbpairs]

Summary

• define the T4 operator as owner only of T4 CRs, runtime Pods, Services, PVC claims, finalizers, and infrastructure conditions
• keep database, storage, ingress, object-store, and observability providers independently owned
• distinguish portable charts from the optional T4 Stack Helm distribution
• preserve the durable Hub, Runtime Wire, and owner-epoch recovery contracts

Verification

• node --test scripts/check-host-ownership.test.mjs
• pnpm dlx prettier@3.6.2 --check docs/T4_ARCHITECTURE.html

Context

This incorporates @usr-bin-roygbiv's architecture feedback and records the Kubernetes ownership boundary before merging his cluster-operator implementation in #115. PR #115 remains preserved unchanged and will be integrated with its authorship intact.