feat(tui): support Windows and WSL UNC paths in file drag-and-drop

[477174]

Summary

Two WSL clipboard/file issues fixed:

1. File drag-and-drop: Dragging files from Windows Explorer into opencode on WSL pasted Windows paths (C:\Users\..., \\wsl$\distro\...) which were treated as plain text instead of file attachments
2. Image clipboard paste: Ctrl+V with an image on the clipboard never worked on WSL because PowerShell can't access the Windows clipboard session from WSL, and WSLg's Wayland bridge was unreachable due to wrong XDG_RUNTIME_DIR

Changes

Commit 1: feat(tui): support Windows and WSL UNC paths in file drag-and-drop

File: packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx

• Add isWindowsPath(), isFilePath(), resolveDroppedPath() helpers
• Convert drive-letter paths (C:\Users\foo) → /mnt/c/Users/foo on WSL
• Convert UNC paths (\\wsl$\Ubuntu\home\foo) → /home/foo on WSL
• Update all 4 paste handler code paths to detect and resolve Windows paths
• Strip double quotes from dropped paths (Windows terminal behavior)
• Zero behavior change on native Unix, native Windows, macOS

Commit 2: fix(tui): fix clipboard image paste on WSL via WSLg Wayland bridge

File: packages/opencode/src/cli/cmd/tui/util/clipboard.ts

• Skip PowerShell clipboard on WSL (always fails — session isolation)
• Fix wl-paste/wl-copy on WSLg: override XDG_RUNTIME_DIR to /mnt/wslg/runtime-dir where the Wayland socket actually lives
• Requires wl-clipboard package (apt install wl-clipboard)

Platform behavior

Scenario	Before	After
WSL + drag from Windows (C:\...)	Plain text ❌	File attached ✅
WSL + drag WSL file via Explorer (\\wsl$\...)	Plain text ❌	File attached ✅
WSL + paste image from clipboard	Silent failure ❌	Image attached ✅ (needs wl-clipboard)
Native Windows	Worked ✅	Still works ✅
Linux/macOS	Worked ✅	Still works ✅

Prerequisites for WSL image paste

sudo apt install wl-clipboard

WSLg must be enabled (default on Windows 11 with recent WSL2).

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