route native file drops to editor vs terminal based on drop surface

[AmethystLiang]

Summary

• Add data-native-file-drop-target attribute to distinguish editor vs terminal drop zones at the preload level
• Preload classifies native OS drops before forwarding via IPC so the renderer can route them correctly — terminal drops insert escaped paths into the active PTY, editor drops open files in tabs
• Falls back to 'editor' for drops on untagged surfaces (sidebar, editor body) to preserve prior open-in-editor behavior

Test plan

• Drag a file from OS onto the terminal pane → path is inserted into the active CLI
• Drag a file from OS onto the tab bar → file opens in the editor
• Drag a file from OS onto the editor body / sidebar → file opens in the editor (fallback)
• Drag multiple files onto the terminal → paths are space-separated
• Verify no regressions with in-app drag/drop (tab reordering, etc.)