Clipboard: rich formats (image + HTML/MIME) beyond plain text

[codymullins]

Problem

Skyline's clipboard is plain text only. A browser eventually needs to copy/paste images and HTML fragments and read arbitrary MIME types. Text covers focused-field copy/cut/paste today, so this is future work.

Current state

• src/Skyline/AppWindow.cs:155 — ClipboardText is a string?.
• src/Skyline/IWindowBackend.cs — text-only on the seam.
• src/Skyline.Interaction.Ui/IClipboard.cs — text-only abstraction.

What's needed

• Extend the clipboard surface to typed data: read/write by MIME type and enumerate available types (keeping the text path backward compatible).
• AppKit NSPasteboard (typed), Win32 clipboard formats, X11 selections / Wayland data-device with MIME types.

Acceptance criteria

• Round-trip text/plain, text/html, and image/png; graceful degradation to text where a format is unavailable.