Drag-to-Resize Pane Implementation

Overview

Add drag-to-resize support for two-pane plugin layouts (sidebar + main content). Users click and drag the divider between panes to resize them.

Prerequisites

• Plugin already has a two-pane layout (sidebar + main content)
• State persistence functions exist in internal/state/state.go (each plugin has its own getter/setter)
• Familiarity with internal/mouse package

Existing Implementations