applet: add pin button for standalone widget in panel

Nate Grahamrequested to merge
work/ngraham/pin-button-for-standalone-widget into master

It's already got one when it's in the System Tray, but not when compact on a panel in standalone form. Add one.

FEATURE: 472728
FIXED-IN: 6.6.0

Screenshot_20251124_212156

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