docs: add Mecatl research note - #54

What is this note about?

Addresses #53 with a research note on Mecatl as a cloud-native agent harness. It covers the provider-agnostic loop, permissions and delegation, durable sessions and event logs, gRPC/HTTP-SSE APIs, the Kubernetes mecak8s runtime, and Cloud Foundry relevance.

Checklist

• My note lives in research/ and uses a lowercase kebab-case filename.
• It starts from research/TEMPLATE.md and has valid frontmatter.
• It has the four required sections.
• I added relevant tags.
• Sources are linked.
• It's on-topic for agentic workloads on Cloud Foundry.