Fix blurry text in LightBulb preview by changing TextFormattingMode to Ideal

[Copilot]

The text above the LightBulb preview was appearing blurry compared to text below due to using TextFormattingMode="Display" instead of TextFormattingMode="Ideal" in the PreviewPane.xaml file.

The issue was caused by the WPF TextOptions.TextFormattingMode being set to Display mode, which uses GDI-compatible font metrics that can result in blurry text rendering, especially on non-integer DPI scaling factors.

This change updates the PreviewPane to use Ideal mode instead, which uses ideal font metrics and provides better text clarity. According to Microsoft's WPF documentation:

• Display mode: Uses GDI-compatible font metrics (can cause blurry text)
• Ideal mode: Uses ideal font metrics (provides crisp text rendering)

The fix is a minimal one-line change that only affects text rendering quality without impacting any other functionality.

Fixes #80181.

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