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/ralph-loop.md

@@ -42,7 +42,7 @@ A [Ralph loop](https://ghuntley.com/ralph/) is an autonomous development workflo
 The minimal Ralph loop — the SDK equivalent of `while :; do cat PROMPT.md | copilot ; done`:
 
 ```csharp
-using GitHub.Copilot.SDK;
+using GitHub.Copilot;
 
 var client = new CopilotClient();
 await client.StartAsync();
@@ -96,7 +96,7 @@ This is all you need to get started. The prompt file tells the agent what to do;
 The full Ralph pattern with planning and building modes, matching the [Ralph Playbook](https://github.com/ClaytonFarr/ralph-playbook) architecture:
 
 ```csharp
-using GitHub.Copilot.SDK;
+using GitHub.Copilot;
 
 // Parse args: dotnet run [plan] [max_iterations]
 var mode = args.Contains("plan") ? "plan" : "build";