doc: add TEA narrative drafts

[MChorfa]

Summary

This PR is a focused split from #235 and contains only text-based TEA notes:

• api-flow/consumer.md
• doc/authorization.md
• doc/tea-requirements.md
• doc/tea-usecases.md
• doc/versioning.md

Scope

• no protobuf or JSON schema files
• no implementation or generated artifacts
• no Excalidraw diagrams

Intent

Keep review on narrative requirements, use cases, authorization, and versioning notes only.

[MChorfa]

This PR is one part of the split from #235, which has been closed in favor of smaller review units.

Related PRs:

• doc: narrow TEA authentication guidance #236 doc: narrow TEA authentication guidance
• spec: add TEA discovery and consumer contract drafts #237 spec: add TEA discovery and consumer contract drafts
• doc: add a short TEA profiles note #238 doc: add a short TEA profiles note
• spec: add TEA publisher and insights service drafts #239 spec: add TEA publisher and insights service drafts
• doc: add TEA narrative drafts #240 doc: add TEA narrative drafts
• doc: add TEA diagrams and graph schema #241 doc: add TEA diagrams and graph schema

[oej]

This pull request is still all over the specification. Please split into narrow pull requests instead of trying to merge something that changes a lot of things. Thank you.