Move the "not ready to migrate" note to the top of the guide

Put it right under the intro as an admonition, matching the "Coming from
v1?" note elsewhere, instead of at the end of the Need Help section
where nobody scrolls to.

No-Verification-Needed: doc-only change

Author: maxisbey

docs/migration.md

@@ -4,6 +4,11 @@ This guide covers the breaking changes introduced in v2 of the MCP Python SDK an
 
 Version 2 of the MCP Python SDK introduces several breaking changes to improve the API, align with the MCP specification, and provide better type safety.
 
+!!! note "Not ready to migrate yet?"
+    The v1.x maintenance line keeps receiving critical bug fixes and security patches, and its
+    documentation is at [/v1/](https://py.sdk.modelcontextprotocol.io/v1/). If your package depends
+    on `mcp`, keep a `<2` upper bound until you've migrated.
+
 ## Find your changes
 
 Every section heading below names the API it affects, so searching this page for the symbol your code uses is the fastest route to the change that broke it. The guide lists changes only: an SDK API not mentioned here behaves as it did in v1, and the "what did not change" summaries — [`MCPServer`](#what-is-unchanged-on-mcpserver), [lowlevel `Server`](#lowlevel-server-what-did-not-change), and [auth](#unchanged-auth-surfaces) — spell out the surfaces most migrators stop to check.
@@ -2877,6 +2882,3 @@ If you encounter issues during migration:
 1. Check the [API Reference](api/mcp/index.md) for updated method signatures
 2. Review the [examples](https://github.com/modelcontextprotocol/python-sdk/tree/main/examples) for updated usage patterns
 3. Open an issue on [GitHub](https://github.com/modelcontextprotocol/python-sdk/issues) if you find a bug or need further assistance
-
-Not ready to migrate yet? The v1.x maintenance line keeps receiving critical bug fixes and security
-patches; its documentation is at [/v1/](https://py.sdk.modelcontextprotocol.io/v1/).