Replace the external clipboard dependency with small macOS, Windows,
and X11 helpers and integrate them into coding-agent.
Run native clipboard operations on worker threads and make command
fallbacks asynchronous. Preserve incremental X11 transfers, legacy text
encodings, native image formats, and existing Wayland and platform tools.
Include native prebuilds with ARM64 page alignment, packaging updates,
and regression coverage.
WSL2/WSLg often provides clipboard images as image/bmp only.
Previously this resulted in invalid PNG files being written.
Now readClipboardImage() converts unsupported formats to PNG
via Photon before returning.
Closes#1109
Based on #1112 by @lightningRalf