Record the Windows beta12 preview candidate

[coneilen]

Summary

Record the immutable, unpublished Windows beta12 preview candidate and its
LFS-aware Dev Box handoff.

Beta10 is failed/superseded. Its attended Dev Box run produced #640–#643. Beta11
was tagged but never built, because its source contained a validation file
committed by mistake (removed in #645). All runtime qualification gates remain
open.

Changes

• Record source/tag/package/payload/executable/provider/toolchain identities for
  0.1.78-windows.beta12 at 1199de5e631ad71e0f2aff47910e668651ad791f.
• Record Hide the console window of zmx children spawned by the Windows shell #640–Remove a committed validation workspace layout and ignore new ones #645, and the workspace-layout-in-current-directory product
  defect that Remove a committed validation workspace layout and ignore new ones #645 does not fix.
• Record the current parity count of 98 surfaces: 60 Validated / 38 Partial,
  after Keep loop bar text clear of its buttons at narrow widths #642 and Start attended loops from the daemon when the Windows shell opens them #643 each downgraded a row.
• Record local validation honestly. Unit, App, scrubbed startup and the
  real-daemon round trip passed; the local live UIA gate failed at different
  menu steps, while exact-head CI passed it.
• Record custody, the offline restore (43/43 LFS) and the 8/8 handoff.
• Move beta10 to history, and keep beta1–beta11 unchanged.

Test plan

RED: windows-shell validation at ab47b46 (pre-#644) -> unit 55/55, App 771/771, scrubbed 5/5, round trip PASS; live UIA gate failed "Turn promotion submenu did not reopen natively"
GREEN: Tools\windows\release.ps1 -Tag 0.1.78-windows.beta12 -> repository verify 1 PASS; extracted setup verify 1 PASS; payload 50; binary reports 0.1.78-windows.beta12 and deferred
REGRESSION: Tools\windows\Tests\ScrubbedShellStartup.Live.Tests.ps1 against the extracted beta12 package binaries -> PASS; executed=5 including registered-project

• Source custody Create and Verify passed with 43 objects for 43 files.
• The file-only offline restore through Restore-GraphCodeSource.ps1 gave the
  exact detached HEAD/tag, zero remotes, a clean status and 43/43 materialized
  LFS files.
• Handoff inventory: 8/8 verified; hashes.sha256 SHA-256
  4afb67e6d381d20ce52e73ae03aca6ac20ac472537bcbe3ca32bc8ffd8abaead.
• Not claimed: a local live-UIA pass, Dev Box results, backend use, terminal
  pixels, destructive operations, Worktrees, Nod, dumps or publication.
• No tag or release was pushed or published.
• macOS make test and make check were not run because this is a
  documentation-only 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