fix(app-nav-btn): fixed relative right position on small screens

[emoral435]

☑️ Resolves #2278

🖼️ Screenshots

🏚️ Before	🏡 After

🚧 Summary

• When the viewport got small in the photos app, the app-navigation-button overflowed to the right of the screen, becoming inaccessible
• To fix this, since the button is positioned relative to the header, I removed some of the negative right positioning on the button

This allows the button to still be in view, while a little tight, and also still allows it to be found with keyboard navigation 👍
Any styling choices can be commented on !

Checklist

Code is properly formatted

Sign-off message is added to all commits

[ ] Tests (unit, integration, api and/or acceptance) are included

[x] Screenshots before/after for front-end changes

[x] Documentation (manuals or wiki) has been updated or is not required

[x] Backports requested where applicable (ex: critical bugfixes)

[emoral435]

For the reviewers - no worries, only one file got changed, and it was a minor change 👀 not some scary 29-file PR

[artonge]

Shouldn't this be fixed in @nc/vue?

[emoral435]

Full transparency - did not know that this was a component within NcVue 👀 but I found it right now, will be changing that! Closing this PR and submitting this change there 👍

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