Delay folder registration until owner restoration

[coneilen]

Summary

Prevents the Windows shell from registering a selected folder before USER32
has finished restoring the picker owner window after IFileDialog::Show
returns.

Changes

• replace the immediate posted completion message with a dedicated one-shot
  window timer
• process queued owner activation/focus messages before changing the project,
  subscription, layout, and daemon registration state
• cancel the timer before dispatch and during window destruction
• extend the real-HWND regression to prove owner restoration precedes exactly
  one completion, cancel is inert, repeated accept is safe, and timer IDs do
  not collide

Test plan

RED: zig test src\App.zig src\AccessibilityProvider.cpp src\FilePicker.c .graphcode-tools\providers\winghostty\zig-out\lib\winghostty-win32-host.lib -target x86_64-windows-msvc --test-filter "folder picker completion waits for native callback unwind" -> expected 0 posted completions, found 1
GREEN: zig test src\App.zig src\AccessibilityProvider.cpp src\FilePicker.c .graphcode-tools\providers\winghostty\zig-out\lib\winghostty-win32-host.lib -target x86_64-windows-msvc --test-filter "folder picker completion waits for native callback unwind" -> 1/1 passed
REGRESSION: pwsh -NoProfile -File Tools\windows\validate.ps1 -Task windows-shell -SkipTrayLive -ShellValidationRoot C:\v5 -SwiftExecutable $env:GRAPHCODE_SWIFT633 -> exit 0; 52/52 sections, App 736/736, Worktree process 21/21, shell smoke, daemon handoff, tray contracts, and full UIA passed

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

The Dev Box reproduced the pre-fix production crash after native Ctrl+O and
Select Folder: daemon registration succeeded once, then the shell terminated
with USER32 0xc0000005 / callback escape 0xc000041d. This Windows host could
not deliver the attended picker-opening accelerator or menu input reliably, so
the post-fix native accept path remains NotExecuted locally and must be rerun
on the Dev Box. No dump was collected or required for this source-level fix.