fix(ux): auto-scroll selected item into view during keyboard navigation in Command Palette and Quick Switcher #1369

Summary

In CommandPaletteDialog (lib/features/command_palette/command_palette_dialog.dart, lines 84–91, 151–196) and QuickSwitcherDialog (lib/features/command_palette/quick_switcher_dialog.dart, lines 131–137, 220–250):

Both dialogs support Arrow Up / Arrow Down keyboard navigation (_move(delta)). However, their ListView.builder widgets do not have a ScrollController and do not scroll to keep the highlighted item in view.

Problem Details

• The modal dialog height is constrained to 360px (itemExtent: 36 / 40), showing at most ~8 visible items at a time.
• When searching schemas or commands with 10+ results, pressing Arrow Down moves _selected beyond index 8.
• Because there is no ScrollController or Scrollable.ensureVisible call, the selection moves off-screen into hidden items.
• The user cannot see what item is currently selected or what command/schema will be executed when pressing Enter.
• Additionally, list items in the builder do not declare Semantics(selected: active), preventing screen readers from announcing which item is currently highlighted.

Scope

• Attach a ScrollController to ListView.builder in both CommandPaletteDialog and QuickSwitcherDialog.
• In _move(delta), compute the target scroll offset based on itemExtent and animate / jump to keep _selected visible in the viewport.
• Wrap items in Semantics(selected: active, button: true).
• Add widget tests verifying that pressing Arrow Down scrolls the list when selection crosses the viewport boundary.