Code Quality: Ensure minimum size for UI elements based on DPI scaling

[seer-by-sentry]

Resolved / Related Issues

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• Closes FILES-APP-3FQ

Steps used to test these changes

Stability is a top priority for Files and all changes are required to go through testing before being merged into the repo. Please include a list of steps that you used to test this PR.

1. Ensured that thumbnail sizes and window dimensions are at least 1 pixel.
2. Modified the AppWindowDPI property to handle cases where the DPI is not immediately available or is invalid, defaulting to 1.0f.
3. Verified that the division by zero error in WinUI's layout is resolved.

[Copilot]

Pull Request Overview

This PR addresses a division by zero error in WinUI's layout system by ensuring minimum UI element sizes based on DPI scaling. The changes prevent crashes when DPI calculations result in zero or negative values by enforcing minimum sizes of 1 pixel for various UI elements.

• Enforces minimum size of 1 pixel for icon thumbnails and window dimensions
• Modifies AppWindowDPI property to handle invalid or unavailable DPI values with a fallback
• Adds defensive programming to prevent layout calculation errors

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
FileThumbnailHelper.cs	Ensures icon size is at least 1 pixel before Win32 icon retrieval
FilePropertiesHelpers.cs	Enforces minimum window dimensions for properties dialog
AppModel.cs	Adds lazy loading and validation for DPI calculation with fallback
WidgetFolderCardItem.cs	Ensures thumbnail size is at least 1 pixel before loading

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