Record Windows beta5 preview candidate

[coneilen]

Summary

Record the immutable, unpublished Windows beta5 preview candidate and its
LFS-aware Dev Box handoff. Beta4 remains failed/superseded after the scrubbed
startup crash; all runtime qualification gates remain open.

Changes

• Record source/tag/package/payload/executable/provider/toolchain identities for
  0.1.78-windows.beta5.
• Record source-custody verification and file-only offline restore with 43/43
  LFS files materialized.
• Record the versioned 8/8 Dev Box handoff inventory and retain beta1 through
  beta4 as immutable, unpublished history.
• Keep Exact artifact complete while Clean installation, Production core flow,
  Useful agent terminal, Reachability/lifecycle, Safe mutations, and Honest
  tester handoff remain open.

Test plan

RED: Test-ScrubbedStartup.ps1 against immutable beta4 with the exact 11-key allowlist -> exit 1; event=fatal detail=EnvironmentVariableNotFound
GREEN: Tools\windows\Tests\ScrubbedShellStartup.Live.Tests.ps1 against packaged beta5 -> 4/4 passed with live shell, daemon, and CLI
REGRESSION: Tools\windows\release.ps1 -Tag 0.1.78-windows.beta5 -> repository verify 1 PASS; extracted setup verify 1 PASS; payload 50

• Source custody Create and Verify: passed with 43 objects for 43 files.
• File-only offline restore: exact detached HEAD/tag, zero remotes, clean status,
  and 43/43 materialized LFS files.
• Handoff inventory: 8/8 hashes verified; hashes.sha256 SHA-256
  2e41b4fe94a944df26110882bac99860b6f8f96ac1578473c406d3826aef39d3.
• No tag or release was pushed or published. No Dev Box, backend, native-client,
  destructive fixture, Worktrees execution, dump, or publication evidence is
  claimed.
• macOS make test and make check were not run because this is a
  documentation-only Windows candidate evidence update.

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