live activity: fix vertical centering on lock screen

GeometryReader as the layout root pinned content top-left, and forcing
maxHeight:.infinity over-claimed the whole proposed height, centring the
content below true vertical centre (bigger gap above) on the Lock Screen.

Demote GeometryReader to a background side-channel that only measures the
slot width for the rich-vs-compact branch; the content stays intrinsic-sized
so the system vertically centres it itself.

FuelBoardWidgets/FuelBoardLiveActivityView.swift

@@ -67,32 +67,46 @@ private struct FuelBoardLiveActivityView: View {
 
     /// Below this ACTUAL proposed width we show the compact strip (CarPlay
     /// small / Watch smart stack); at/above it we show the full card. The
-    /// decision is made from the real space the system hands the body via
-    /// GeometryReader, NOT from ViewThatFits ideal-width measurement — the
-    /// latter is broken for truncating text (a long station name inflates the
-    /// "ideal" width past the iPhone Lock Screen and collapses the full card).
+    /// decision is made from the real width the system hands the body, read
+    /// via a background GeometryReader — NOT ViewThatFits ideal-width
+    /// measurement (that's broken for truncating text: a long station name
+    /// inflated the "ideal" width past the iPhone Lock Screen and collapsed
+    /// the full card).
     private let compactWidthThreshold: CGFloat = 280
 
+    /// Measured slot width (drives the rich-vs-compact branch). Measured in a
+    /// background GeometryReader so it does NOT act as the layout container:
+    /// a GeometryReader root pins content top-left, and forcing a
+    /// maxHeight:.infinity frame on it over-claims the whole proposed height,
+    /// centring the content below true vertical centre (bigger gap above) on
+    /// the Lock Screen. Measuring behind the scenes keeps the content
+    /// intrinsic-sized so the system vertically centres it itself.
+    @State private var slotWidth: CGFloat = 400
+
     var body: some View {
         Link(destination: context.state.mapsURL) {
-            GeometryReader { geo in
+            Group {
                 // Branch on the ACTUAL proposed width. iPhone/iPad offer the
                 // full Lock Screen width (>= threshold) → rich card, no matter
                 // how long the station name is. Truly small slots (CarPlay /
                 // Watch) offer much less → compact strip.
-                Group {
-                    if geo.size.width >= compactWidthThreshold {
+                if slotWidth >= compactWidthThreshold {
                     richBody
                 } else {
                     compactBody
                 }
             }
-                // A GeometryReader hands its content the FULL proposed frame
-                // (content is otherwise pinned top-left), so centre the card
-                // within that space — keeps the Lock Screen content vertically
-                // aligned instead of sitting high.
-                .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .center)
+            // Fill the card width so the background measure reads the real
+            // slot, not the intrinsic content width.
+            .frame(maxWidth: .infinity)
+            // Side-channel width measurement — never the layout container.
+            .background(
+                GeometryReader { geo in
+                    Color.clear
+                        .onAppear { slotWidth = geo.size.width }
+                        .onChange(of: geo.size.width) { _, w in slotWidth = w }
                 }
+            )
         }
     }