Fix per-user preview pane not working by detecting actual installation scope

[Copilot]

Problem

The preview pane modules were hardcoded to always register as per-user installations (installPerUser = true), regardless of whether PowerToys was actually installed per-machine or per-user. This caused preview handlers to be registered in the wrong registry scope, making them non-functional when PowerToys was installed per-machine.

Root Cause

Two key locations used hardcoded per-user values:

• powerpreview.cpp:27 - PowerPreviewModule constructor
• modulesRegistry.h:273,288 - getAllOnByDefaultModulesChangeSets() and getAllModulesChangeSets()

Solution

Replaced hardcoded true values with dynamic detection using the existing registry::install_scope::get_current_install_scope() function:

// Before:
const bool installPerUser = true;

// After:  
const bool installPerUser = (registry::install_scope::get_current_install_scope() == registry::install_scope::InstallScope::PerUser);

Changes Made

1. powerpreview.cpp: Added #include <common/utils/registry.h> and replaced hardcoded installation scope detection
2. modulesRegistry.h: Updated both registry ChangeSet functions to use dynamic scope detection

Expected Behavior

• Per-Machine Installation: Preview handlers registered in HKEY_LOCAL_MACHINE
• Per-User Installation: Preview handlers registered in HKEY_CURRENT_USER
• Result: Preview pane functionality works correctly for both installation types

Impact

• ✅ Fixes preview pane functionality for per-machine PowerToys installations
• ✅ Maintains compatibility with per-user installations
• ✅ Affects both runtime module behavior and MSI installer registry setup
• ✅ No breaking changes to existing functionality

Fixes #22.

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