Restore Explorer shell if setup leaves it stopped

[YellowNest]

Summary

Restore the Windows Explorer desktop shell when setup completes successfully but Restart Manager leaves it stopped.

The bootstrapper now records whether the current interactive session is actually using explorer.exe as its desktop shell before launching msiexec. After a successful MSI transaction it gives Restart Manager a short grace period to restore Explorer normally. If the shell is still missing, setup launches %WINDIR%\explorer.exe once as a fallback.

The recovery is intentionally conservative:

• it only runs if Explorer was the desktop shell before setup
• it verifies the shell belongs to the same session
• it does nothing for alternative shells or non-interactive deployment sessions
• it does nothing after failed or reboot-required MSI outcomes
• it does not loop if Explorer itself is crashing

This keeps Restart Manager as the primary recovery mechanism and only repairs the failure case described in #2070.

Verification

A full fork PR build completed successfully for exact commit 2c79a8a558a3e2748d69aff0d02a3add5305b468, including:

• Build binaries
• Build installers
• Build setup and symbols

Build:
https://github.com/YellowNest/Open-Shell-Menu/actions/runs/37226898693

Fixes #2070

[ale5000-git]

@YellowNest
@ge0rdi
This thing happened to me in the past on Windows 10.

The situation was that there was an explorer.exe open (seen in task manager) but no desktop and no application bar.
Opening explorer.exe again just opened a folder.
Instead the correct solution was to terminate the existent explorer.exe and then open it again.

Is there a way to detect a missing application bar with explorer.exe opened?