Enhancement: Wire optional Azure DevOps polling module

[Unthred]

Problem

Infrastructure/AzureDevOps/ exists but is not wired into tray startup (optional future module per BUILD_STATUS_MONITOR_PLAN.md).

Acceptance criteria

• Settings schema for org URL and pipelines (or remove dead code)
• Tray integration behind explicit opt-in
• ADR if persistence/auth approach is chosen

Surfaces

Infrastructure, TrayApp, docs