feat: add Copy, Paste, Select All commands to Edit menu (#8954)

## Summary

- Add Copy, Paste, and Select All commands to the Edit menu for
mobile/touch users and accessibility
- Menu-based copy uses LiteGraph internal clipboard; existing Ctrl+C/V
behavior is unchanged

## Changes

- `useCoreCommands.ts`: Register three new commands (`CopySelected`,
`PasteFromClipboard`, `SelectAll`)
- `coreMenuCommands.ts`: Add menu entries under Edit (between Undo/Redo
and Clear Workflow)
- `useCoreCommands.test.ts`: Add unit tests for the new commands

### AS IS
<img width="260" height="176" alt="스크린샷 2026-02-18 오후 5 44 14"
src="https://github.com/user-attachments/assets/8c9c86e1-55cc-411b-9d42-429001e04630"
/>


### TO BE
<img width="516" height="497" alt="스크린샷 2026-02-19 오후 5 07 28"
src="https://github.com/user-attachments/assets/a2047541-582f-4520-a08f-98c6e532d29f"
/>


## Test plan

- [x] Verify Copy/Paste/Select All appear in Edit menu
- [x] Select nodes → Edit > Copy → Edit > Paste → nodes duplicated
- [x] Edit > Select All → all canvas items selected
- [x] Copy with no selection → no-op (no error)
- [x] Existing Ctrl+C/V keyboard shortcuts still work

Fixes #2892

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8954-feat-add-Copy-Paste-Select-All-commands-to-Edit-menu-30b6d73d365081ec9270ed2a562eaf0b)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/constants/coreMenuCommands.ts

@@ -14,6 +14,14 @@ export const CORE_MENU_COMMANDS = [
     ]
   ],
   [['Edit'], ['Comfy.Undo', 'Comfy.Redo']],
+  [
+    ['Edit'],
+    [
+      'Comfy.Canvas.CopySelected',
+      'Comfy.Canvas.PasteFromClipboard',
+      'Comfy.Canvas.SelectAll'
+    ]
+  ],
   [['Edit'], ['Comfy.ClearWorkflow']],
   [['Edit'], ['Comfy.OpenClipspace']],
   [