fix(opensidian): use Backquote key code for terminal shortcut

[Gautam-aman]

Summary

Fixes terminal toggle shortcut detection on macOS.

The terminal shortcut handler currently checks KeyboardEvent.key === '\'when handlingCmd + /`Ctrl + . On some macOS keyboard layouts and configurations, the key value may differ even though the physical backquote key is pressed.

This change switches the shortcut detection to use KeyboardEvent.code === 'Backquote', which is layout-independent and consistently identifies the physical backquote key.

Changes

• Replaced e.key === '\'withe.code === 'Backquote'` in the terminal shortcut handler.
• Preserved existing support for both metaKey (macOS Command key) and ctrlKey.

Why

The UI and onboarding text indicate that ⌘ + \`` should toggle the terminal, but users have reported that only Ctrl + ``works. UsingKeyboardEvent.code provides more reliable shortcut detection across macOS keyboard layouts.

Fixes #1718

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[Gautam-aman]

I've opened a PR for this issue. The fix updates terminal shortcut detection to use KeyboardEvent.code ("Backquote") instead of KeyboardEvent.key, which should improve reliability for Cmd + ` on macOS. Please let me know if you'd like me to adjust the approach.