docs: update MCP SDK version from 2.0.0-M3 to 2.0.0-RC1 in documentation

Author: codeboyzhou

docs/index.md

@@ -57,7 +57,7 @@ This SDK is especially suitable for the following scenarios:
 - **ASYNC vs SYNC** — `type: ASYNC` selects the async MCP server API; your annotated methods stay blocking Java wrapped in `Mono.fromCallable(...)`. See [Getting Started — Runtime model](./getting-started.md#runtime-model-and-stability).
 - **Singleton components** — one instance per component class, shared across concurrent requests; keep handlers stateless or thread-safe.
 - **Required YAML** — `instructions` must be non-blank; when `mode` is `STREAMABLE`, the `streamable` transport section must be present and complete.
-- **MCP SDK 2.0.0-M3** — built on a pre-release milestone; pin versions and retest when upgrading.
+- **MCP SDK 2.0.0-RC1** — built on a pre-release milestone; pin versions and retest when upgrading.
 
 ## 📖 Getting Started