docs: rewrite server-initiated request flows for Multi Round-Trip Requests (MRTR) #3042

Where was this agreed?

Requested by maintainer David Soria Parra as part of preparing the modelcontextprotocol.io documentation for the 2026-07-28 specification release.

Description

The 2026-07-28 spec release replaces server-initiated requests with Multi Round-Trip Requests (MRTR). The sampling and elicitation diagrams and prose still show server-sent requests.

Files to update:

• docs/docs/learn/client-concepts.mdx — rewrite the elicitation/sampling diagrams and prose to the InputRequiredResult/inputRequests flow
• docs/docs/learn/architecture.mdx — update client-primitive descriptions away from server-sent sampling/createMessage/elicitation/create calls
• docs/docs/tools/debugging.mdx — reword the -32602 sampling/elicitation troubleshooting entry for MRTR

Part of the 2026-07-28 release documentation tracking (milestone: 2026-07-28 Specification Release).