docs: mark fix-nightly-native-macos-windows Done after #277

[enricopiovesan]

Summary

• Mark fix-nightly-native-macos-windows Done (fix: nightly macOS Sendable + WinUI PresentationMapper compile #277) on the start plan.

Governing Spec

• Docs-only board hygiene. No UI business logic. No private Traverse internals.

Project Item

• Ticket ID: fix-nightly-native-macos-windows
• Item: PVTI_lADOEbiBt84BbzAzzg4Iq4I — Done / Unassigned after fix: nightly macOS Sendable + WinUI PresentationMapper compile #277

Definition of Done

• AGENTS.md start-plan row is Done (fix: nightly macOS Sendable + WinUI PresentationMapper compile #277), not In Progress
• Production baseline N/A

Validation

• bash scripts/ci/repository_checks.sh (existing required file)

Checklist

Traceability

• Project 2 Agent Unassigned + Status Done
• AGENTS.md start-plan updated
• Blocked set unchanged

Production baseline (platform / runtime-client PRs)

• N/A — docs hygiene only

Architecture

• No business logic added to UI layer
• No private Traverse internals imported