feat(nav): replace Map+Instruments with Map+Layers in bottom nav

Layers acts as an action button — shows LayerPickerSheet and snaps
back to Map so it never stays selected. Instruments tab removed;
sheet expand/collapse via swipe as before.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

3 files changed, 23 insertions, 7 deletions

diff --git a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
index de1f4dd..0309364 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
@@ -130,10 +130,17 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
                     bottomSheetBehavior.state = BottomSheetBehavior.STATE_COLLAPSED
                     true
                 }
-                R.id.nav_instruments -> {
-                    hideOverlays()
-                    bottomSheetBehavior.isHideable = false
-                    bottomSheetBehavior.state = BottomSheetBehavior.STATE_EXPANDED
+                R.id.nav_layers -> {
+                    // Action button — show picker then snap back to Map
+                    val currentStyle = loadedStyleFlow.value
+                    if (currentStyle != null) {
+                        LayerPickerSheet(
+                            manager = layerManager,
+                            onBaseChanged = { preset -> layerManager.setBasePreset(currentStyle, preset) },
+                            onWindChanged = { enabled -> layerManager.setWindEnabled(currentStyle, enabled) }
+                        ).show(supportFragmentManager, "layer_picker")
+                    }
+                    bottomNav.post { bottomNav.selectedItemId = R.id.nav_map }
                     true
                 }
                 R.id.nav_log -> {
diff --git a/android-app/app/src/main/res/drawable/ic_layers.xml b/android-app/app/src/main/res/drawable/ic_layers.xml
new file mode 100644
index 0000000..f86f83a
--- /dev/null
+++ b/android-app/app/src/main/res/drawable/ic_layers.xml
@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="?attr/colorOnSurface"
+        android:pathData="M11.99,18.54L4.62,12.81 3,14.07l9,7 9,-7-1.63,-1.27-8.38,5.74zM12,16l8.36,-6.54L22,8.07l-10,-7-10,7 1.63,1.39L12,16z"/>
+</vector>
diff --git a/android-app/app/src/main/res/menu/bottom_nav_menu.xml b/android-app/app/src/main/res/menu/bottom_nav_menu.xml
index b29fb08..e7fc15d 100644
--- a/android-app/app/src/main/res/menu/bottom_nav_menu.xml
+++ b/android-app/app/src/main/res/menu/bottom_nav_menu.xml
@@ -5,9 +5,9 @@
         android:icon="@drawable/ic_map"
         android:title="Map" />
     <item
-        android:id="@+id/nav_instruments"
-        android:icon="@drawable/ic_instruments"
-        android:title="Instruments" />
+        android:id="@+id/nav_layers"
+        android:icon="@drawable/ic_layers"
+        android:title="Layers" />
     <item
         android:id="@+id/nav_log"
         android:icon="@drawable/ic_log"