[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.

.github/workflows/conformance-weekly.yaml

@@ -26,7 +26,7 @@ jobs:
             baseline: conformance-baseline-2025-11-25.yml
           - spec-version: '2026-07-28'
             dist-tag: alpha
-            path: '/stateless'
+            path: '/'
             baseline: conformance-baseline-2026-07-28.yml
     steps:
       - uses: actions/checkout@v7

.github/workflows/pipeline.yaml

@@ -109,7 +109,7 @@ jobs:
             path: '/'
             baseline: conformance-baseline-2025-11-25.yml
           - spec-version: '2026-07-28'
-            path: '/stateless'
+            path: '/'
             baseline: conformance-baseline-2026-07-28.yml
 
     steps: