Feature request: Add chat:redo action for keybinding support

Summary

Claude Code's chat input supports chat:undo but has no corresponding chat:redo action. Once text is undone in the input box, there is no way to redo/restore it.

Current behavior

• chat:undo exists and can be bound to a key (e.g. ctrl+shift+z)
• No chat:redo action exists in the keybinding system
• After undoing text, it is permanently lost with no way to recover it

Expected behavior

A chat:redo action should be available to bind (e.g. to ctrl+y or ctrl+shift+z) that restores text that was undone, matching standard editor undo/redo behavior.

Use case

Standard text editing muscle memory — users expect Ctrl+Z / Ctrl+Shift+Z (or Ctrl+Y) to undo and redo changes to the chat input.