mcp(docs[copy_mode]): note pane.cmd injects -t pane_id

Inline comments at both ``pane.cmd`` sites in ``copy_mode.py`` so a
future contributor doesn't "fix" the missing ``-t pane.pane_id`` back
in. ``libtmux.Pane.cmd`` injects ``-t self.pane_id`` already; the
manual prefix produced ``tmux <verb> -t %X -t %X ...`` and tmux's
argparser silently kept the last ``-t``. The CHANGES file documents
the original cleanup; this lifts the explanation onto the line that
needs it.

Author: tony

src/libtmux_mcp/tools/pane_tools/copy_mode.py

@@ -55,6 +55,8 @@ def enter_copy_mode(
         session_id=session_id,
         window_id=window_id,
     )
+    # libtmux's Pane.cmd injects ``-t pane.pane_id``; passing it again
+    # produced the duplicated ``-t %X -t %X`` shape tmux silently accepted.
     pane.cmd("copy-mode")
     if scroll_up is not None and scroll_up > 0:
         pane.cmd(
@@ -107,6 +109,7 @@ def exit_copy_mode(
         session_id=session_id,
         window_id=window_id,
     )
+    # See enter_copy_mode: Pane.cmd injects ``-t pane.pane_id`` already.
     pane.cmd("send-keys", "-X", "cancel")
     pane.refresh()
     return _serialize_pane(pane)