Support OSC 52 clipboard read for image data (binary/base64)

[ohkimur]

Claude Code (Anthropic's CLI) uses OSC 52 to read clipboard contents for image paste. Currently this works for text but not images.

Current behavior: Pasting an image does nothing (text paste works fine with clipboard-read = allow)

Expected: Respond to OSC 52 read requests with base64-encoded image data when clipboard contains an image.