Stabilize Windows UIA focus live gate

[coneilen]

Summary

Hardens the Windows native UI Automation worktree-row focus assertion against shared CI desktop-focus churn without weakening the assertion or changing product behavior.

Changes

• Preserve the existing 30-second focus-retention polling loop and hard failure/diagnostics.
• Reorder each polling iteration to settle briefly (40ms) after ActivateWindow before calling SetFocus, so the row's focus assertion is the last action before sampling FocusedElement.
• Keep a final bounded nudge (300ms settle + short recheck) before the hard failure, using the same settle-then-focus-then-check ordering.

Notes on iteration

A first attempt (commit 7db72cd) only added a trailing final nudge without reordering; it still reproduced the failure on hosted windows-spikes (https://github.com/scgopi/GraphCode/actions/runs/35476483960/job/105986495560) with the identical symptom, showing the interfering refocus lands after SetFocus inside every loop iteration, not only at the loop boundary. Commit a3d6910 reorders each iteration accordingly.

Test plan

RED: Tools/windows/validate.ps1 -Task all -SkipTrayLive -SkipWslRemoteE2E on PR #387 commit 1ed41ca -> failed in windows-spikes with worktree row could not retain focus against concurrent desktop focus changes; focused=Text Area:Text Area (https://github.com/scgopi/GraphCode/actions/runs/35475073552/job/105985602192)
GREEN: PowerShell parser on Tools/windows/uia-live-gate.ps1 at commit a3d6910 -> passed with no parse errors; pwsh -NoProfile -File Tools/windows/Tests/ValidationRunner.Tests.ps1 -> PASS
REGRESSION: pwsh -NoProfile -File Tools/windows/validate.ps1 -Task windows-shell -SkipTrayLive -> reached the pre-UIA Swift release build and stopped on the known local SDK limitation missing required modules: '_complex', 'ucrt'; hosted windows-spikes runs the complete gate and is the authoritative pass/fail signal for this change

Checklist

• I have read the Contributing Guidelines
• I have signed off my commits (git commit -s) per the DCO
• Tests pass locally (make test) — not applicable to this Windows-only test-infrastructure change; focused validation is documented above
• Code follows the existing style (git diff --check)
• I added the focused synchronization behavior after reproducing the intended RED failure in the linked same-source CI run, and iterated after the first fix attempt was disproven by hosted CI