Fix Comparer CLI startup and validate Store MSIX

[chammoru]

Summary

• fix Comparer startup when invoked with multiple command-line file paths
• expose one Viewer entry point in the Store MSIX while retaining the bundled Comparer workflow
• make Viewer locate bundled Comparer relative to its installed executable
• add a Windows Store validation workflow that builds the MSIX, smoke-tests install/uninstall, captures screenshots, and runs WACK

Validation

• Successful Windows 2022 run: https://github.com/chammoru/Q1View/actions/runs/26398002142
• Comparer remained running after opening reference.png and encoded.jpg from the command line
• Viewer launched bundled Comparer while running from a different working directory
• MSIX installed and uninstalled cleanly
• WACK Application count now passes after using a single Store entry point
• WACK overall result is WARNING: Blocked executables is an optional Desktop Bridge test and DPIAwarenessValidation reports a warning

Microsoft documents Desktop Bridge optional tests as informational and not used to evaluate Store onboarding: https://learn.microsoft.com/en-us/windows/uwp/debug-test-perf/windows-desktop-bridge-app-tests

Fixes #16
Relates to #27