fix(tui): support clipboard image paste with proper filename on WSL2

[mmdsnb]

Summary

Fixes clipboard image pasting in WSL2 terminal environment. When users copy image files from Windows file manager and paste into OpenCode TUI, the full Windows path (e.g., D:\temp\image.png) was being displayed instead of just the filename.

Changes

1. Enhanced Clipboard Reading (clipboard.ts)

• Added support for ContainsFileDropList() to detect copied image files on Windows
• Automatically extract filename from Windows file paths
• Convert Windows paths to WSL paths (D:\... → /mnt/d/...)
• Return filename in Clipboard.Content interface

2. Fixed Paste Event Handling (prompt/index.tsx)

• Call event.preventDefault() immediately in onPaste to prevent default text insertion
• Check clipboard for images before processing pasted text
• Manually handle text insertion for all paste scenarios
• Use extracted filename instead of "clipboard" label

Testing

Tested on WSL2 with Windows Terminal:

1. ✅ Copy image file from Windows file manager (Ctrl+C) → Paste (Ctrl+V)
2. ✅ Drag image file from file manager to terminal window
3. ✅ Copy image from application (e.g., browser) → Paste
4. ✅ Normal text pasting still works correctly

Before

D:\temp\ScreenShot_2026-01-13_191354_854.png [Image 1]

After

ScreenShot_2026-01-13_191354_854.png [Image 1]

Technical Details

• PowerShell script now outputs FILEPATH: prefix to indicate file path source
• Path conversion only happens in WSL environment (detected via os.release())
• No performance impact on normal text pasting (< 500 chars check optimization)

Fixes #issue-number-if-exists