Update .NET Copilot SDK cookbook for GitHub.Copilot.SDK 1.0 (#2021)

* Update .NET Copilot SDK cookbook for GitHub.Copilot.SDK 1.0

Align the dotnet copilot-sdk cookbook recipes and docs with the 1.0.1 release:

- Namespace GitHub.Copilot.SDK -> GitHub.Copilot

- MCP config uses Dictionary<string, McpServerConfig> + McpStdioServerConfig (drop Type discriminator)

- StopAsync no longer returns an error list; wrap graceful shutdown in try/catch

- GetMessagesAsync -> GetEventsAsync with event pattern matching

- LogLevel string -> CopilotLogLevel.Error enum

* Address PR review: clarify package/namespace, default event case, MCP stdio wording

- Note that the GitHub.Copilot.SDK package exposes the GitHub.Copilot namespace in each recipe

- Add a default case + note to the GetEventsAsync history example so other event kinds are not silently dropped

- Refine accessibility-report docs to describe a local stdio MCP server (McpStdioServerConfig via npx)

* Address re-review: add using for event types, note StopAsync throw behavior

cookbook/copilot-sdk/dotnet/recipe/ralph-loop.cs

@@ -1,6 +1,7 @@
 #:package GitHub.Copilot.SDK@*
 
-using GitHub.Copilot.SDK;
+// The GitHub.Copilot.SDK package exposes the GitHub.Copilot namespace.
+using GitHub.Copilot;
 
 // Ralph loop: autonomous AI task loop with fresh context per iteration.
 //