Ctrl+V image paste should warn when xclip/xsel missing on Linux

Description

On Linux, the input prompt shows a tooltip: "press Ctrl+V to paste images". However, this feature silently fails if xclip (or xsel) is not installed — there's no error message or indication of what's wrong.

Expected behavior

Either:

• The tooltip should mention the dependency: "press Ctrl+V to paste images (requires xclip)"
• Or when paste fails due to missing clipboard tool, show an actionable error: "Image paste requires xclip. Install with: sudo apt install xclip"

Environment

• Platform: Linux (Zorin OS / Ubuntu-based)
• Terminal: gnome-terminal, Kitty
• Claude Code: latest

Steps to reproduce

1. Fresh Linux install without xclip or xsel
2. Copy an image to clipboard
3. Press Ctrl+V in Claude Code prompt
4. Nothing happens — no error, no feedback
5. Install xclip → image paste works

The fix is trivial for the user once they know, but the silent failure is confusing.