Add media navigation hotkeys and confirmation alternative

[andersendsa]

Summary

• Added standard hotkeys for navigating between media items: Left Arrow for Previous Media, Right Arrow for Next Media.
• Added Enter as an alternative hotkey for saving/finalizing annotations and predictions, as requested.
• Updated the useKeyboardNavigation hook to handle ArrowLeft and ArrowRight.
• Updated the SecondaryToolbar to listen for the new alternative confirmation hotkey.
• Updated the HotkeysList component so these new shortcuts display properly in the UI

Closes : #6273

How to test

1. Open the application UI and navigate to your project.
2. Click on the Dataset tab to view your media gallery.
3. Select an image or video frame to open the Annotator view.
4. Test Navigation: Make sure you aren't focused on a text box, then press the Left Arrow key. You should navigate to the previous media item. Press the Right Arrow key. You should navigate to the next media item.
5. Test Boundaries: Press the Left Arrow on the very first item, and the Right Arrow on the last item. Verify that the UI stays on the current item and no errors occur.
6. Test Save Action: Create or modify an annotation (or select a classification label) so the confirmation button becomes enabled. Press the Enter key.
7. Verify that the annotation is successfully saved and the UI automatically advances to the next media item.
8. Verify Hotkey Menu: Click the "Hotkeys" (keyboard) icon in the toolbar.
9. Check that "Previous media" (ArrowUp or ArrowLeft) and "Next media" (ArrowDown or ArrowRight) are now listed.
10. Check that the "Save annotations/predictions" entry now reads ENTER or CMD+S (or CTRL+S).

Checklist

• The PR title and description are clear and descriptive
• I have manually tested the changes
• All changes are covered by automated tests
• All related issues are linked to this PR (if applicable)
• Documentation has been updated (if applicable)

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[andersendsa]

Hi @dwesolow , @jpggvilaca pls let me know if this pr needs any changes or if it is good to merge