fix: update shortcut alt+N -> option+N on macOS

[XMLHexagram]

Summary by Sourcery

Bug Fixes:

• Correct the keyboard shortcut display from 'Alt+N' to '⌥+N' for macOS users.

[sourcery-ai]

Reviewer's Guide by Sourcery

The PR updates the keyboard shortcut display text for the cover wall feature to show the correct modifier key symbol (⌥) on macOS while keeping 'Alt' for other platforms. This is implemented by adding a platform check and using conditional text rendering.

No diagrams generated as the changes look simple and do not need a visual representation.

File-Level Changes

Change	Details	Files
Added platform-specific shortcut text display for the cover wall feature	Imported the Platform class from dart:io Updated ShortcutText widget to conditionally display '⌥+N' on macOS and 'Alt+N' on other platforms	lib/widgets/playback_controller/constants/controller_items.dart

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[sourcery-ai]

Hey @XMLHexagram - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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