Moving a Group selects nodes inside, but copying does not

### Feature Idea

**Description:**

When moving a Group by dragging its title bar, all nodes within the Group's boundaries automatically move together. This indicates that ComfyUI already has the logic to determine which nodes belong to a Group based on their position within the Group's boundaries.

However, when copying a Group (selecting the Group and pressing Ctrl+C), the nodes inside are **not** automatically included. Users must manually select all nodes within the Group before copying.

**Expected behavior:**
Copying a Group should automatically include all nodes within its boundaries, just like moving does.

**Current behavior:**
- Moving a Group → nodes inside move together ✓
- Copying a Group → nodes inside are NOT included ✗

This inconsistency is confusing and adds unnecessary steps to the workflow. It would be a significant quality-of-life improvement if the copy behavior matched the move behavior.

### Existing Solutions

_No response_

### Other

_No response_

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*This issue is transferred from: https://github.com/comfyanonymous/ComfyUI/issues/11308*

Original issue was created by @lcxsssx at 2025-12-13T13:01:31.000Z

**Original Comments:**

@lcxsssx:

A large workflow is usually composed of several small groups. Some useful groups now require manually selecting each node within them one by one to copy the entire group, which is very troublesome

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-7454-Moving-a-Group-selects-nodes-inside-but-copying-does-not-2c86d73d3650818f9367f2a82d7290a9) by [Unito](https://www.unito.io)

No files or tests are named. Start by tracing the existing group-drag movement logic and the Ctrl+C copy path, then verify how nodes inside group boundaries are selected; done means copying a selected group includes its contained nodes without manual selection.

Written by the indexing model from the issue text.