Refresh MCP runtime dependencies

[dsghi]

Summary

• refresh the MCP/server-facing runtime packages, including the Azure Functions MCP extension, C# MCP SDK, Functions worker, Cosmos, IdentityModel, and Data Protection servicing lines
• refresh test tooling while leaving the xUnit v3 migration separate
• document the intentional Application Insights WorkerService 2.x hold because DevBrain still uses the direct Functions isolated Application Insights integration path

Validation

• dotnet test devbrain.slnx --no-restore
• dotnet list devbrain.slnx package --vulnerable --include-transitive
• dotnet list devbrain.slnx package --outdated --highest-patch
• dotnet list devbrain.slnx package --deprecated