[codex] Generate SDK snippets from OpenAPI examples

[HavenDV]

Summary

• generate an autosdk.generated-examples.json manifest from OpenAPI request and response examples
• synthesize C# SDK snippets when the request shape is clear and fall back to .http snippets otherwise
• teach autosdk docs sync to merge generated snippets with handwritten examples and preserve per-example language/setup metadata
• add focused unit and CLI integration coverage for snippet generation and docs sync

Validation

• dotnet test src/tests/AutoSDK.UnitTests/AutoSDK.UnitTests.csproj --filter "FullyQualifiedName~SnippetGenerationTests|FullyQualifiedName~DocsSyncTests"
• dotnet test src/tests/AutoSDK.UnitTests/AutoSDK.UnitTests.csproj --filter "FullyQualifiedName~HttpTests|FullyQualifiedName~Tests.ExtensionParsing"
• dotnet test src/tests/AutoSDK.IntegrationTests.Cli/AutoSDK.IntegrationTests.Cli.csproj --filter "FullyQualifiedName~Generate_WithOpenApiExamples_EmitsGeneratedSnippetManifest"
• dotnet build src/libs/AutoSDK.CLI/AutoSDK.CLI.csproj /p:TreatWarningsAsErrors=true

Closes #237