Support multiple Azure DevOps organization PATs

[viamus]

Summary

• Add multi-organization Azure DevOps configuration with one PAT per organization
• Resolve the selected organization per MCP tool call through an optional organization argument
• Keep backward compatibility with existing single-organization settings
• Update appsettings, Docker/.env examples, installer, README, and config tests

Validation

• dotnet build src\Viamus.Azure.Devops.Mcp.Server\Viamus.Azure.Devops.Mcp.Server.csproj --no-restore
• git diff --cached --check

Note

• dotnet test Solution.slnx --no-restore is currently blocked by local NuGet PackageSourceMapping: NU1100 resolving Microsoft.AspNetCore.Mvc.Testing (>= 10.0.0) for net10.0.