fix: Track popover height as explicit SwiftUI dependency

Adds .onChange(of: popoverHeight) so SwiftUI registers the computed
value as a dependency of the .frame modifier. Without it, some Release
builds appear to skip the frame update when only the underlying @State
(chromeHeight / usageContentHeight) changes — the panel locks at its
initial-render height and shows visible empty bands above the header
and below the footer. Reported on 1.5.3, did not reproduce locally
even in Release config, so this is a defensive belt-and-suspenders
fix rather than a verified root-cause fix. Also adds a small
[Popover] log line for future diagnosis.