feat: expose litegraph internal keybindings (#9459)

## Summary

Migrate hardcoded litegraph canvas keybindings (Ctrl+A/C/V, Delete,
Backspace) into the customizable keybinding system so users can remap
them via Settings > Keybindings.

## Changes

- **What**: Register Ctrl+A (SelectAll), Ctrl+C (CopySelected), Ctrl+V
(PasteFromClipboard), Ctrl+Shift+V (PasteFromClipboardWithConnect),
Delete/Backspace (DeleteSelectedItems) as core keybindings in
`defaults.ts`. Add new `PasteFromClipboardWithConnect` command. Remove
hardcoded handling from litegraph `processKey()`, the `app.ts` Ctrl+C/V
monkey-patch, and the `keybindingService` canvas forwarding logic.

Fixes #1082
Fixes #2015

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9459-feat-expose-litegraph-internal-keybindings-31b6d73d3650819a8499fd96c8a6678f)
by [Unito](https://www.unito.io)

src/composables/useCoreCommands.ts

@@ -905,6 +905,14 @@ export function useCoreCommands(): ComfyCommand[] {
         app.canvas.pasteFromClipboard()
       }
     },
+    {
+      id: 'Comfy.Canvas.PasteFromClipboardWithConnect',
+      icon: 'icon-[lucide--clipboard-paste]',
+      label: () => t('Paste with Connect'),
+      function: () => {
+        app.canvas.pasteFromClipboard({ connectInputs: true })
+      }
+    },
     {
       id: 'Comfy.Canvas.SelectAll',
       icon: 'icon-[lucide--lasso-select]',
@@ -919,6 +927,12 @@ export function useCoreCommands(): ComfyCommand[] {
       label: 'Delete Selected Items',
       versionAdded: '1.10.5',
       function: () => {
+        if (app.canvas.selectedItems.size === 0) {
+          app.canvas.canvas.dispatchEvent(
+            new CustomEvent('litegraph:no-items-selected', { bubbles: true })
+          )
+          return
+        }
         app.canvas.deleteSelected()
         app.canvas.setDirty(true, true)
       }