Add unit settings, wind particles toggle, and recenter-to-top

- New UnitPrefs: persisted C/F, ft/m, hPa/inHg, kt/mph/kph — defaults to °F
- InstrumentHandler now accepts raw values (knots, metres, hPa, °C) and formats
  via UnitPrefs on every update
- LayerPickerSheet expanded with wind particles toggle and unit chip selectors;
  wrapped in ScrollView to handle the additional height
- MapLayerManager tracks particlesEnabled (persisted); setParticlesEnabled() added
- MainActivity: caches last raw values so refreshUnits() can reformat everything
  instantly when the user changes a unit without waiting for new sensor data
- Recenter button moved to top (below HUD strip) so it's never obscured by the
  bottom sheet or bottom nav
- Unit label TextViews given IDs in HUD and instrument sheet for live updates

https://claude.ai/code/session_01HXPjBsogsJVRwCiekDGkJX

1 files changed, 2 insertions, 2 deletions

diff --git a/android-app/app/src/main/res/layout/activity_main.xml b/android-app/app/src/main/res/layout/activity_main.xml
index 5147506..5943949 100644
--- a/android-app/app/src/main/res/layout/activity_main.xml
+++ b/android-app/app/src/main/res/layout/activity_main.xml
@@ -90,10 +90,10 @@
                 android:visibility="gone"
                 app:cornerRadius="20dp"
                 app:elevation="20dp"
-                app:layout_constraintBottom_toBottomOf="parent"
+                app:layout_constraintTop_toBottomOf="@id/nav_hud"
                 app:layout_constraintEnd_toEndOf="parent"
                 app:layout_constraintStart_toStartOf="parent"
-                android:layout_marginBottom="24dp" />
+                android:layout_marginTop="8dp" />
 
         </androidx.constraintlayout.widget.ConstraintLayout>