[Idea] Add interactive pane transfer between workspaces (drag-detach + API)

[yuloop]

Summary

Enable users to detach a pane from one workspace and attach it to another via drag-and-drop, plus corresponding WebSocket API methods for programmatic pane movement.

Proposed Features

Mouse Interaction

• Drag a pane title bar to detach it from its current workspace
• Drop target indicators show available workspaces
• Visual feedback during drag operation

WebSocket API

New API methods for programmatic pane movement between workspaces.

Use Cases

• Moving a long-running terminal session to a different workspace without closing/reopening
• Setting up new workspaces by dragging existing panes rather than recreating them
• Power users who reorganize workspaces frequently

Key Design Consideration

Live pane state (running process, scrollback) must be preserved during transfer — no detach/re-attach as a fresh pane.