feat: drag files from explorer sidebar to terminal

[nwparker]

Summary

• File explorer sidebar items are now draggable
• Dropping a file onto the terminal pastes its shell-escaped absolute path into the active pane
• Uses a custom MIME type (text/x-orca-file-path) so it doesn't interfere with native OS file drops

Changes

• FileExplorer.tsx: Added draggable and onDragStart to file/folder buttons
• TerminalPane.tsx: Added onDragOver/onDrop handlers that send the path via PTY transport
• preload/index.ts: Skip global drop handler for in-app drags so React's onDrop fires

Test plan

• Drag a file from the explorer onto the terminal → path appears at cursor
• Drag a file with spaces in the name → path is properly shell-escaped
• Native OS file drop still works as before
• Dragging a folder also works (pastes folder path)

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