feat: support file drag-and-drop into terminal nodes

[zuxinrui]

Summary

• Add drag-and-drop support for files from the system file manager into terminal/agent nodes
• Dropped files have their absolute paths pasted at the cursor, matching native terminal behavior (GNOME Terminal, iTerm2, Windows Terminal, etc.)
• Uses Electron's webUtils.getPathForFile() (sandbox-safe) to resolve file paths, with shell-special character escaping via single-quote wrapping
• Delegates to xterm's terminal.paste() for correct bracketed paste mode handling

Details

Problem: In native terminals, dragging a file into the window pastes its path. In OpenCove, dragging files into agent/terminal nodes had no effect — xterm.js does not handle HTML5 drag-and-drop events, and no custom handler existed.

Changes (3 files, ~40 lines):

File	Change
src/.../TerminalNode.tsx	Add dragover/drop event listeners on the terminal container DOM element
src/app/preload/index.ts	Expose webUtils.getPathForFile() via opencoveApi.filesystem
src/app/preload/index.d.ts	Add type declaration for getPathForFile

Design decisions:

• webUtils.getPathForFile() instead of File.path — the latter returns empty string in sandbox mode
• terminal.paste() instead of ptyWriteQueue.enqueue() — automatically handles bracketed paste mode
• stopPropagation() on both events — prevents the canvas-level image import handler from interfering
• Shell escaping uses single-quote wrapping (handles spaces, $, backticks, etc.)

Test plan

• Drag a single file → path appears at cursor
• Drag a file with spaces in path → path is single-quoted
• Drag multiple files → space-separated paths
• Drag a directory → path appears (same as file)
• Drag an image to canvas (not terminal) → existing image import still works
• Ctrl+V paste still works normally

🤖 Generated with Claude Code

[CLAassistant]

All committers have signed the CLA.

[DeadWaveWave]

感谢贡献！PR 还需要处理一下文件冲突问题

[zuxinrui]

@DeadWaveWave 文件冲突已经解决，如果有其他问题请随时message，感谢！