Use canonical release-notes template for RC and GA (modelcontextprotocol#2800)

RC: full description matching prior -RC releases — draft links,
draft changelog, and the 'not final' NOTE block with the
version-negotiation pointer.

GA: same structure with versioned URLs and the NOTE block dropped.

Both now write the body via a heredoc to --notes-file so the markdown
(backticks, blockquote) survives intact. $VERSION comes from env and is
regex-validated before these steps run.

Author: localden

.github/workflows/cut-release.yml

@@ -52,15 +52,23 @@ jobs:
           GH_TOKEN: ${{ github.token }}
           TARGET_SHA: ${{ github.sha }}
         run: |
+          cat > /tmp/notes.md <<EOF
+          This release marks the **release candidate (RC)** \`${VERSION}\` revision of the Model Context Protocol.
+
+          The specification is available in [draft form](https://modelcontextprotocol.io/specification/draft).
+
+          For a detailed overview of changes, see [${VERSION} draft changelog](https://modelcontextprotocol.io/specification/draft/changelog).
+
+          >[!NOTE]
+          >**To users and implementers:** this specification is not final. Changes may be introduced between the RC and the final release. SDKs will adopt this version at their own pace, and the prior version of the spec may remain in use for an undetermined amount of time.
+          >
+          >Refer to the [Version Negotiation documentation](https://modelcontextprotocol.io/specification/draft/basic/lifecycle#version-negotiation) to learn about the process for clients and servers to determine the version of the protocol being used.
+          EOF
           gh release create "${VERSION}-RC" \
             --target "$TARGET_SHA" \
             --prerelease \
             --title "MCP ${VERSION} RC" \
-            --notes "Release candidate for the ${VERSION} revision of the Model Context Protocol specification.
-
-          The RC content is the current draft: https://modelcontextprotocol.io/specification/draft
-
-          Please file issues against SEPs in this milestone before the final cut."
+            --notes-file /tmp/notes.md
 
       - name: Summary
         run: |

.github/workflows/publish-release.yml

@@ -44,11 +44,15 @@ jobs:
             echo "tag ${VERSION} already exists — skipping"
             exit 0
           fi
+          cat > /tmp/notes.md <<EOF
+          This release marks the \`${VERSION}\` revision of the Model Context Protocol.
+
+          The specification is available at [modelcontextprotocol.io/specification/${VERSION}](https://modelcontextprotocol.io/specification/${VERSION}).
+
+          For a detailed overview of changes, see the [${VERSION} changelog](https://modelcontextprotocol.io/specification/${VERSION}/changelog).
+          EOF
           gh release create "$VERSION" \
             --target "$TARGET_SHA" \
             --latest \
             --title "MCP ${VERSION}" \
-            --notes "Model Context Protocol specification ${VERSION}.
-
-          https://modelcontextprotocol.io/specification/${VERSION}
-          Changelog: https://modelcontextprotocol.io/specification/${VERSION}/changelog"
+            --notes-file /tmp/notes.md