* fix(panel): open represented provider from standalone icon

The standalone panel identity had no activation handler, so clicking it
fell through to the background toggle and reopened the popup's previous
tab instead of the displayed provider. Give it the same provider-aware
activation as provider meters, with pointer, keyboard, and accessible
activation, keeping the popup toggle when no provider is selected and a
no-op in noninteractive previews.

Constraint: reuse the existing openProviderFromPanel path
Confidence: high
Scope-risk: narrow

* fix(panel): show keyboard focus ring on standalone provider icon