docs(lanes): align contract lane stack with Argo/Tekton and Foreman/Katello

[mdheller]

Summary

• add lane stack alignment notes for workstation/CI contracts
• document the intended split between Argo/Tekton execution/orchestration and Foreman/Katello provisioning/content/promotion
• capture the immediate backlog for execution-profile and content-source metadata in lane contracts

Why

The current repo already states that it is the contract/conformance layer, not the runner or image builder. This PR makes the execution/build/content split explicit so future lane schema work lands in the right shape.

Follow-on

• add schema fields for execution profile and content-source requirements
• add good example lane contracts that reference Argo/Tekton execution and Foreman/Katello content prerequisites
• add conformance checks for unsupported execution profiles or missing content metadata