Fix broken links to MCP Tasks specification (#1594)

Co-authored-by: Tarek Mahmoud Sayed <tarekms@ntdev.microsoft.com>

Author: tarekgh

docs/concepts/tasks/tasks.md

@@ -13,7 +13,7 @@ uid: tasks
 
 The Model Context Protocol (MCP) supports [task-based execution] for long-running operations. Tasks enable a "call-now, fetch-later" pattern where clients can initiate operations that may take significant time to complete, then poll for status and retrieve results when ready.
 
-[task-based execution]: https://modelcontextprotocol.io/specification/draft/basic/utilities/tasks
+[task-based execution]: https://modelcontextprotocol.io/seps/1686-tasks
 
 ## Overview
 
@@ -601,4 +601,4 @@ While this file-based approach demonstrates the pattern, production systems shou
 - <xref:ModelContextProtocol.InMemoryMcpTaskStore>
 - <xref:ModelContextProtocol.Protocol.McpTask>
 - <xref:ModelContextProtocol.Protocol.McpTaskStatus>
-- [MCP Tasks Specification](https://modelcontextprotocol.io/specification/draft/basic/utilities/tasks)
+- [MCP Tasks Specification](https://modelcontextprotocol.io/seps/1686-tasks)

docs/list-of-diagnostics.md

@@ -23,7 +23,7 @@ If you use experimental APIs, you will get one of the diagnostics shown below. T
 
 | Diagnostic ID | Description |
 | :------------ | :---------- |
-| `MCPEXP001` | Experimental APIs for features in the MCP specification itself, including Tasks and Extensions. Tasks provide a mechanism for asynchronous long-running operations that can be polled for status and results (see [MCP Tasks specification](https://modelcontextprotocol.io/specification/draft/basic/utilities/tasks)). Extensions provide a framework for extending the Model Context Protocol while maintaining interoperability (see [SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133)). |
+| `MCPEXP001` | Experimental APIs for features in the MCP specification itself, including Tasks and Extensions. Tasks provide a mechanism for asynchronous long-running operations that can be polled for status and results (see [MCP Tasks specification](https://modelcontextprotocol.io/seps/1686-tasks)). Extensions provide a framework for extending the Model Context Protocol while maintaining interoperability (see [SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133)). |
 | `MCPEXP002` | Experimental SDK APIs unrelated to the MCP specification itself, including subclassing `McpClient`/`McpServer` (see [#1363](https://github.com/modelcontextprotocol/csharp-sdk/pull/1363)) and `RunSessionHandler`, which may be removed or change signatures in a future release (consider using `ConfigureSessionOptions` instead). |
 
 ## Obsolete APIs