docs: sync concepts/index.md with toc.yml — add Tasks entry and align Stateless/Stateful placement

Agent-Logs-Url: https://github.com/modelcontextprotocol/csharp-sdk/sessions/752b2e50-d1f9-4f2a-b42c-c17b84b9e7b1

Co-authored-by: jeffhandley <1031940+jeffhandley@users.noreply.github.com>

Author: Copilot

docs/concepts/index.md

@@ -14,10 +14,12 @@ Install the SDK and build your first MCP client and server.
 | - | - |
 | [Capabilities](capabilities/capabilities.md) | Learn how client and server capabilities are negotiated during initialization, including protocol version negotiation. |
 | [Transports](transports/transports.md) | Learn how to configure stdio, Streamable HTTP, and SSE transports for client-server communication. |
+| [Stateless and Stateful](stateless/stateless.md) | Learn when to use stateless vs. stateful mode for HTTP servers and how to configure sessions. |
 | [Ping](ping/ping.md) | Learn how to verify connection health using the ping mechanism. |
 | [Progress tracking](progress/progress.md) | Learn how to track progress for long-running operations through notification messages. |
 | [Cancellation](cancellation/cancellation.md) | Learn how to cancel in-flight MCP requests using cancellation tokens and notifications. |
 | [Pagination](pagination/pagination.md) | Learn how to use cursor-based pagination when listing tools, prompts, and resources. |
+| [Tasks](tasks/tasks.md) | Learn how to use task-based execution for long-running operations that can be polled for status and results. |
 
 ### Client Features
 
@@ -36,6 +38,5 @@ Install the SDK and build your first MCP client and server.
 | [Prompts](prompts/prompts.md) | Learn how to implement and consume reusable prompt templates with rich content types. |
 | [Completions](completions/completions.md) | Learn how to implement argument auto-completion for prompts and resource templates. |
 | [Logging](logging/logging.md) | Learn how to implement logging in MCP servers and how clients can consume log messages. |
-| [Stateless and Stateful](stateless/stateless.md) | Learn when to use stateless vs. stateful mode for HTTP servers and how to configure sessions. |
 | [HTTP Context](httpcontext/httpcontext.md) | Learn how to access the underlying `HttpContext` for a request. |
 | [MCP Server Handler Filters](filters.md) | Learn how to add filters to the handler pipeline. Filters let you wrap the original handler with additional functionality. |