📝 docs: say when the menu bar icon actually appears

The interface reference said the icon turns grey when the network drops
and takes an orange badge when a client needs a sign-in, which reads as
though the icon sits alongside the cells. StatusItemBuilder sets
showsIcon to cells.isEmpty, so it replaces them: a provider that is signed
out beside one that is working shows no icon at all, and the reader is
left watching the wrong thing.

Claude-Session: https://claude.ai/code/session_01CGckDFXvufWVmRH4uyE4z8

Author: gaborbernat

website/content/reference/interface.md

@@ -20,8 +20,14 @@ green to red. Four formats exist:
 | Mini bars         | Provider glyph plus tiny bars, one cell per provider carrying its windows                          |
 | Custom            | Any template built from tokens such as `{cell}`, `{pct1}` and `{reset}`                            |
 
-Windows at 0% stay hidden until you ask for them. The icon turns grey when the network drops and takes an orange badge
-when a client needs a sign-in. The countdown redraws once a second, and only while the template references `{reset}`.
+Windows at 0% stay hidden until you ask for them. The countdown redraws once a second, and only while the template
+references `{reset}`.
+
+The app icon replaces the cells rather than sitting beside them, so it appears only when there is nothing to show: no
+provider has reported yet, every selected window is hidden, or **Fit to space** has stepped down to its narrowest
+layout. It is grey while a provider is offline and orange while one needs a sign-in, sign-in winning when both are true.
+A provider that is signed out beside one that is working leaves the cells on screen and no icon, so watch the Usage tab
+rather than the menu bar for that.
 
 With **Fit to space** on, the app notices when macOS hides the item (typically behind the notch once a busy app menu
 takes the left half of the bar) and steps down through narrower layouts: the configured format, stacked, one cell per