fix(a11y): enable keyboard tab closure and expand pointer target size in QueryaTabStrip #1372

Summary

In Querya UI Kit QueryaTabStrip (lib/shared/widgets/querya_tab_strip.dart, lines 294–317):

The tab close button is rendered as a raw GestureDetector containing a 13px close icon with padding: EdgeInsets.all(1):

1. Pointer Target Violation: The effective hit area is only ~15x15 px. This violates WCAG 2.1 AA (minimum 24x24 px target size) and AAA (minimum 44x44 px target size), making it difficult to click precisely on high-DPI desktop screens without hitting the tab itself.
2. Keyboard inaccessible: The close button cannot be reached via Tab navigation, and when keyboard focus is on a tab (_onKeyEvent), pressing Delete or Backspace does not close the focused tab (only arrowLeft, arrowRight, home, end are handled).
3. No semantic label: Missing Semantics(button: true, label: 'Close $label tab').

Scope

• In QueryaTabStrip._onKeyEvent, add handlers for LogicalKeyboardKey.delete and LogicalKeyboardKey.backspace to trigger widget.onClose!(index).
• Expand the close button tap target to at least 24x24 px padding.
• Wrap the close button in material.Semantics(button: true, label: 'Close $label tab') with a tooltip.
• Add regression widget test in test/shared/widgets/querya_tab_strip_test.dart.