Arc browser - Side Panel API unsupported

[anna-st-40]

When running InboxWhiz in Arc, the extension installs normally and clicking the icon opens Gmail, but the InboxWhiz UI never appears.

Arc does not currently support the Chrome Side Panel API. InboxWhiz renders entirely inside the side panel, so without side panel support, there is nowhere for the UI to mount.

We need to implement a fallback rendering method for browsers that don’t support side panels.

[art-shen]

Also, a few other Chrome-based browsers popular in some regions don't support the sidebar. E.g., it happens in YandexBrowser