feat: add C motion to change to end of line

[reobin]

• mirrors D: deletes from cursor to end of line and enters insert mode
• works with the existing register and undo flow

[leohenon]

Thanks, looks good. Just one visual-mode edge case: C now runs while already in visual mode and ignores the selection.

Repro:

1. Type one two three
2. Normal mode, cursor on two
3. Press v, w, C
4. Compare with v, w, c

Expected: visual C should not fall through to normal-mode C.
Actual: it deletes from cursor to end of line, ignoring the visual selection.

A minimal fix would be to handle shifted C in the existing visual c branch:

if ((key === "c" || isShifted(event, "c")) && !hasModifier(event)) {
  begin(() => {
    const reg = deleteSelection(input.textarea(), lw, a ?? undefined)
    if (reg) setRegister(reg)
    clearSelection(input.textarea())
    input.state.setMode("insert")
  })
  event.preventDefault()
  return true
}

Note: For closer Vim accuracy, visual C should be a linewise change. But visual D currently behaves like visual d, not linewise delete, so I don’t think we need to solve that yet, just the minimal consistency fix is enough here.

A future change could make both visual D and visual C linewise but I dont think thats necessary for now.

[reobin]

@leohenon I ended up making it vim-accurate for C and D. it will do linewise now.