Link the released 2026-07-28 spec and point migrators at /v1/

The README banner still linked the spec's release-candidate blog post;
the specification is now published, so link it directly. Also give
the migration guide's help section the same pointer to the v1.x
maintenance-line docs that index.md and whats-new.md already carry.

No-Verification-Needed: doc-only change

Author: maxisbey

README.md

@@ -14,7 +14,7 @@
 </div>
 
 > [!NOTE]
-> **This is v2 of the MCP Python SDK, the current stable release line.** It is a major rework of the SDK, both to support the [2026-07-28 MCP specification](https://blog.modelcontextprotocol.io/posts/2026-07-28-release-candidate/) (and every earlier revision) and to fix long-standing architectural issues. Coming from v1? See [What's new in v2](https://py.sdk.modelcontextprotocol.io/whats-new/) for the tour of what changed and the [migration guide](https://py.sdk.modelcontextprotocol.io/migration/) for every breaking change.
+> **This is v2 of the MCP Python SDK, the current stable release line.** It is a major rework of the SDK, both to support the [2026-07-28 MCP specification](https://modelcontextprotocol.io/specification/2026-07-28) (and every earlier revision) and to fix long-standing architectural issues. Coming from v1? See [What's new in v2](https://py.sdk.modelcontextprotocol.io/whats-new/) for the tour of what changed and the [migration guide](https://py.sdk.modelcontextprotocol.io/migration/) for every breaking change.
 >
 > **Not ready to migrate?** v1.x lives on the [`v1.x` branch](https://github.com/modelcontextprotocol/python-sdk/tree/v1.x), continues to receive critical bug fixes and security patches, and is documented at <https://py.sdk.modelcontextprotocol.io/v1/>. Since `pip install mcp` now installs 2.x, keep a `<2` upper bound on your requirement (for example `mcp>=1.28,<2`) until you've migrated.
 >

docs/migration.md

@@ -2877,3 +2877,6 @@ 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/).