README: update module structure & key decisions with mcp-json removal #38

Job	Run time
Client Conformance (initialize)	1m 7s
Client Conformance (sse-retry)	1m 4s
Server Conformance	1m 9s
Client Conformance (tools_call)	58s
Client Conformance (elicitation-sep1034-client-defaults)	56s
	5m 14s

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