[Docs][Examples][CI] Document and gate the 2026-07-28 lifecycle (#457)

docs/stateless-lifecycle.md walks the revision end to end - per-request
_meta, server/discover, multi round-trip requests, caching and subscriptions
- and a runnable example on each side shows what that looks like in code.

CI matrixes both conformance roles over both revisions. --spec-version is
cumulative across the dated revisions, so 2025-11-25 covers the two before
it; 2026-07-28 is not cumulative with them and needs its own run against its
own baseline. The runner is pinned so a PR only goes red for reasons in the
PR, and conformance-weekly tracks the moving target instead - on both
revisions, since the draft scenarios ship only on the alpha dist-tag.

The Inspector cannot reach a modern-lifecycle server (it opens with
initialize), so the example is covered by integration tests instead: one
drives it with hand-built HTTP the way a conforming client would, one drives
it with this SDK's client, and one drives the single endpoint from both eras.

Makefile

@@ -55,7 +55,7 @@ conformance-draft-server:
 	@echo "Waiting for server to start..."
 	@sleep 5
 	rm -rf tests/Conformance/results-2026-07-28
-	cd tests/Conformance && $(CONFORMANCE) server --url http://localhost:8000/stateless --suite all --spec-version 2026-07-28 --expected-failures conformance-baseline-2026-07-28.yml --output-dir results-2026-07-28 || true
+	cd tests/Conformance && $(CONFORMANCE) server --url http://localhost:8000/ --suite all --spec-version 2026-07-28 --expected-failures conformance-baseline-2026-07-28.yml --output-dir results-2026-07-28 || true
 	php tests/Conformance/score.php server 2026-07-28 results-2026-07-28
 	docker compose -f tests/Conformance/Fixtures/docker-compose.yml down