FB-01: fix ambient GPS's first fix not correcting the initial zoom-2

Emulator verification caught a real bug the widget tests missed: the
shell background map builds before any location fix has resolved, so
ambientPosition starts null and the initial camera locks at zoom 2.
The first fix to arrive only re-centered (preserving that stale zoom
forever) instead of also jumping to ambientZoom.

lib/src/ui/components/ride_map.dart

@@ -153,10 +153,19 @@ class _RideMapState extends State<RideMap> with WidgetsBindingObserver {
     } else if (widget.ambientPosition != null &&
         widget.ambientPosition != old.ambientPosition) {
       // FB-01: no recorded path yet -- chase the ambient GPS fix instead, the same way
-      // a recording is chased above.
+      // a recording is chased above. The *first* fix has to also correct the zoom, not
+      // just the center: the very first build (before any fix has arrived) has no
+      // ambient position yet either, so `bounds == null` locks the initial camera at
+      // zoom 2 -- without this, every later fix would re-center at that same
+      // never-corrected zoom 2 forever, since a plain re-center only ever preserves
+      // whatever zoom the map is already at.
+      final isFirstFix = old.ambientPosition == null;
       WidgetsBinding.instance.addPostFrameCallback((_) {
         if (!mounted || !_following) return;
-        _controller.move(widget.ambientPosition!, _controller.camera.zoom);
+        _controller.move(
+          widget.ambientPosition!,
+          isFirstFix ? ambientZoom : _controller.camera.zoom,
+        );
       });
     }
   }