Record the beta2 Windows preview candidate

[coneilen]

Summary

Records the independently reverified 0.1.78-beta2 Windows preview replacement candidate, its immutable artifact and handoff identities, the #604 Worktrees preview guard evidence, and the remaining six open qualification gates. Keeps beta1 as immutable custody evidence, #560 and #587 open, and the 98/62/36 parity ledger unchanged.

Part of #560

Changes

• Replaces beta1 as the active qualification candidate with the exact Guard Worktrees in the Windows preview #604 merge and beta2 package, manifest, source-bundle, approval, plan, and handoff hashes.
• Records the preview-only -Dworktrees-deferred safety boundary, exact deferred message, zero inspection attempts, and the limits of that evidence.
• Preserves beta1 custody history, provider pins, issue states, unpublished/unpushed status, and all NotExecuted Dev Box/native/backend/lifecycle evidence.

Test plan

RED: PowerShell pre-change beta2 candidate contract -> failed: beta2 active candidate record missing; beta1 remains the active candidate
GREEN: PowerShell beta2 active and beta1 superseded contract -> passed
REGRESSION: pwsh -NoProfile -File Tools\windows\Tests\PreviewCore.Tests.ps1 -Case All -> 37/37 passed; no production flight ran

• Parity ledger parser -> 98 total / 62 Validated / 36 Partial / 0 other statuses.
• pwsh -NoProfile -File Tools\windows\validate.ps1 -Task privacy -> passed.
• git diff --check and changed-file scope contract -> passed; only investigation/windows-preview-release-plan.md changed.
• macOS make test and make check were not run because this is a Windows investigation documentation-only change; no macOS or product source changed.

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