Record Windows beta6 preview candidate

[coneilen]

Summary

Record the immutable, unpublished Windows beta6 preview candidate and its
LFS-aware Dev Box handoff. Beta5 remains failed/superseded after the attended
pre-window GDI+ hang; all runtime qualification gates remain open.

Changes

• Record source/tag/package/payload/executable/provider/toolchain identities for
  0.1.78-windows.beta6.
• Record the Prevent GDI+ startup from blocking Windows shell #628 blocking-GDI RED/GREEN evidence and exact-head CI result.
• 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
  beta5 as immutable, unpublished history.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: Tools\windows\Tests\GdiplusStartup.Live.Tests.ps1 before #628 -> live process, no native window, 80 observations under exact 11 keys
GREEN: Tools\windows\Tests\GdiplusStartup.Live.Tests.ps1 at beta6 source -> PASS; executed=1; observations=2; native window appeared
REGRESSION: Tools\windows\release.ps1 -Tag 0.1.78-windows.beta6 -> repository verify 1 PASS; extracted setup verify 1 PASS; payload 50

• Packaged beta6 scrubbed startup: 4/4 passed with developer-tool paths
  excluded.
• 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
  513c9e1138d193426f255c93e789bcc048e2aff252783e1c6e97cd88fd5fef09.
• No tag or release was pushed or published. No Dev Box, backend, native-client,
  destructive fixture, Worktrees execution, Nod, 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