feat: add default keybindings for toggle mode and assets panel (#8593)

## Summary
Add default keyboard shortcuts for mode toggle and assets panel access.

## Changes
- **Ctrl+Shift+A**: Toggle between Simple Mode and Graph Mode
(`Comfy.ToggleLinear`)
- **A**: Open/toggle assets panel (`Workspace.ToggleSidebarTab.assets`)
- Show keybinding in ModeToggle button tooltip (e.g. "Simple Mode
(Ctrl+Shift+A)")

## Keybinding Rationale
- `A` follows the existing pattern: `w` (workflows), `n` (node-lib), `m`
(model-lib)
- `Ctrl+Shift+A` chosen because:
  - Ctrl+Shift is the standard modifier pattern for toggle commands
  - "A" mnemonic for "App mode"
  - Does not conflict with existing keybindings

## Testing
- Verified typecheck passes
- Verified lint passes

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Tooltips now show dynamic keyboard shortcut suffixes for mode and tab
controls.
  * Added keyboard shortcut: A — toggles the assets sidebar.
  * Added keyboard shortcut: Ctrl+Shift+A — toggles linear mode.

* **Localization**
* Added a localized shortcut suffix template so displayed shortcuts
respect translations.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8593-feat-add-default-keybindings-for-toggle-mode-and-assets-panel-2fc6d73d36508172bd6ed3378f43de55)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>

src/locales/en/main.json

@@ -1,5 +1,6 @@
 {
   "g": {
+    "shortcutSuffix": " ({shortcut})",
     "user": "User",
     "you": "You",
     "currentUser": "Current user",