Record Windows beta4 preview candidate

[coneilen]

Summary

Records the replacement 0.1.78-windows.beta4 exact artifact after the Dev Box
folder-picker crash and #624 lifetime fix.

Changes

• mark Windows beta3 failed/superseded and immutable
• record beta4 source/tag, package, executable, provider, and toolchain hashes
• record 43/43 offline LFS custody restore and the verified 8/8 handoff
• keep the native Ctrl+O Dev Box rerun and all other external gates open
• preserve the 98/62/36 parity ledger

Test plan

RED: Select-String -Path investigation\windows-preview-release-plan.md -Pattern 2fede5a before edit -> 0 matches
GREEN: Select-String -Path investigation\windows-preview-release-plan.md -Pattern 2fede5a after edit -> replacement candidate recorded
REGRESSION: PowerShell count of investigation\ui-parity-matrix.md status rows -> VALIDATED=62 PARTIAL=36

Checklist

• I have read the Contributing Guidelines
• I have signed off my commits (git commit -s) per the DCO
• Tests pass locally (make test)
• Code follows the existing style (make check)
• I added the test/contract before the implementation and observed the intended RED failure

Documentation-only change. Candidate package/setup verification, custody
restore, handoff inventory, and exact-head #624 CI are recorded in the plan.