Polish global search clear control with Lucide icon

[masarray]

Field issue

The global search clear affordance in IEC 61850 Signal Selection used a raw × text glyph inside the generic MiniChipButton style. On the current Windows/DPI layout it looked visually heavy, slightly clipped/off-center, and unlike a modern embedded search-field clear control.

Fix

• Replace the raw multiplication-sign glyph with the existing vector LucideX resource.
• Use a dedicated 28×28 DIP embedded hit target with a centered 14×14 Lucide icon.
• Transparent at rest; subtle ARSAS blue-gray hover/pressed surfaces and an internal blue keyboard-focus ring.
• Remove the permanent mini-chip chrome so the clear affordance visually belongs to the search field rather than looking like a toolbar button.
• Hide the clear control automatically while the global search is empty; it appears only when there is text to clear.
• Preserve the existing ClearGlobalFilter_Click behavior.
• Add AutomationProperties.Name="Clear global search" and keep the tooltip concise.
• Keep clipping disabled on the clear control so DPI antialias edges are not cut.

Regression coverage

Adds an XAML regression guard that locks the Lucide resource, 28 DIP hit target, 14 DIP icon, empty-search visibility trigger, accessibility name, and absence of the legacy Content="×" / MiniChipButton implementation.

Final branch contains only SignalSelectionWizardWindow.xaml and the regression test; temporary patch tooling was removed before PR creation.

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