[FEAT] Support for the Kitty drag-and-drop protocol (OSC 72)

Issue description

Please add support for the Kitty drag-and-drop protocol (OSC 72) allowing applications running inside tmux to use drag-and-drop when the outer terminal supports it (as Kitty and iTerm2 do).

This should work in both directions: forwarding DnD events from the terminal to the appropriate pane and forwarding DnD requests from applications to the outer terminal.

The protocol is stateful and includes terminal-coordinate information, so some pane routing and coordinate translation may be required, but the goal should be transparent support for applications using the protocol.

Required information

• tmux version (tmux -V): tmux 3.7c
• Platform (uname -sp): Darwin arm
• Terminal in use (xterm, rxvt, etc): Kitty 0.48.2, iTerm2 3.7.1
• $TERM inside tmux (echo $TERM): tmux-256color
• $TERM outside tmux (echo $TERM): xterm-kitty for Kitty, xterm-256color for iTerm2