Improve accessibility of list items for Talkback screen reader

[keymapper-ai]

Closes #1369

Summary

• Drag handle content descriptions: The drag handle icons in trigger key list items and action list items previously had contentDescription = null. They now use the existing drag_handle_for string resource (e.g. "Drag handle for Volume Up") so TalkBack announces them meaningfully.
• Custom accessibility actions for reordering: Added onMoveUp and onMoveDown parameters to TriggerKeyListItem and ActionListItem. When reordering is enabled, "Move up" and "Move down" custom accessibility actions are registered via Modifier.semantics { customActions = ... } so TalkBack users can reorder items without performing drag gestures. The first item only shows "Move down" and the last item only shows "Move up".
• New string resources: accessibility_action_move_up ("Move up") and accessibility_action_move_down ("Move down") added to strings.xml.

Files changed

• base/src/main/res/values/strings.xml — new string resources
• base/src/main/java/.../trigger/TriggerKeyListItem.kt — drag handle label + move up/down accessibility actions
• base/src/main/java/.../actions/ActionListItem.kt — drag handle label + move up/down accessibility actions
• base/src/main/java/.../trigger/BaseTriggerScreen.kt — passes move callbacks to TriggerKeyListItem
• base/src/main/java/.../actions/ActionsScreen.kt — passes move callbacks to ActionListItem
• CHANGELOG.md — updated

Known limitations / areas for human review

• The SortBottomSheetContent.kt drag handle already used drag_handle_for correctly and was not changed.
• Strings are only provided in English; translations will need to be added for other locales.
• The move actions operate by swapping adjacent items (index ↔ index±1). This matches the existing drag-and-drop behavior, but reviewers should confirm the onMove semantics are consistent with how the ViewModel handles reordering.

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