feat: position properties panel opposite to sidebar (#7647)

## Problem

When sidebar is positioned on the right, the properties panel also
appears on the right, causing both panels to compete for space and
creating a poor layout.

## Solution

Properties panel now dynamically positions itself opposite to the
sidebar:
- Sidebar left → Properties panel right (default)
- Sidebar right → Properties panel left

## Changes

- Modified `LiteGraphCanvasSplitterOverlay.vue` to conditionally render
properties panel based on sidebar location
- Updated splitter refresh key to recalculate layout when sidebar
position changes
- Added dynamic close button icon in `RightSidePanel.vue` that points in
the correct direction

## Testing

- Created E2E tests to verify positioning behavior
- Manually verified visual behavior in browser

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7647-feat-position-properties-panel-opposite-to-sidebar-2ce6d73d365081049683e74c8d03dbdd)
by [Unito](https://www.unito.io)

src/locales/en/main.json

@@ -648,6 +648,7 @@
     "box": "Box"
   },
   "sideToolbar": {
+    "sidebar": "Sidebar",
     "themeToggle": "Toggle Theme",
     "helpCenter": "Help Center",
     "logout": "Logout",