feat: add wind/current map overlay and weather forecast on startup

Implements the wind/current map overlay and 7-day weather forecast
display that loads on application launch:

Data layer:
- Open-Meteo API (free, no key): WeatherApiService + MarineApiService
- Moshi-annotated response models (WeatherResponse, MarineResponse)
- WeatherRepository: parallel async fetch, Result<T> error propagation
- Domain models: WindArrow (with beaufortScale/isCalm) + ForecastItem
  (with weatherDescription/isRainy via WMO weather codes)

Presentation layer:
- MainViewModel: StateFlow<UiState> (Loading/Success/Error),
  windArrow and forecast streams
- MainActivity: runtime location permission, FusedLocationProvider
  GPS fetch on startup, falls back to SF Bay default
- MapFragment: MapLibre GL map with wind-arrow SymbolLayer;
  icon rotated by wind direction, size scaled by speed in knots
- ForecastFragment + ForecastAdapter: RecyclerView ListAdapter
  showing 7-day hourly forecast (time, description, wind, temp, precip)

Resources:
- ic_wind_arrow.xml vector drawable (north-pointing, rotated by MapLibre)
- BottomNavigationView: Map / Forecast tabs
- ViewBinding enabled throughout

Tests (TDD — written before implementation):
- WindArrowTest: calm detection, direction normalisation, Beaufort scale
- ForecastItemTest: weatherDescription, isRainy for WMO codes
- WeatherApiServiceTest: MockWebServer request params + response parsing
- WeatherRepositoryTest: MockK service mocks, data mapping, error paths
- MainViewModelTest: Turbine StateFlow assertions for all state transitions

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

4 files changed, 153 insertions, 0 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
new file mode 100644
index 0000000..757dbdb
--- /dev/null
+++ b/android-app/app/src/main/res/layout/activity_main.xml
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.coordinatorlayout.widget.CoordinatorLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+
+    <androidx.fragment.app.FragmentContainerView
+        android:id="@+id/fragment_container"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:layout_marginBottom="56dp" />
+
+    <com.google.android.material.bottomnavigation.BottomNavigationView
+        android:id="@+id/bottom_nav"
+        android:layout_width="match_parent"
+        android:layout_height="56dp"
+        android:layout_gravity="bottom"
+        android:background="?attr/colorSurface"
+        app:menu="@menu/bottom_nav_menu" />
+
+</androidx.coordinatorlayout.widget.CoordinatorLayout>
diff --git a/android-app/app/src/main/res/layout/fragment_forecast.xml b/android-app/app/src/main/res/layout/fragment_forecast.xml
new file mode 100644
index 0000000..aca38ba
--- /dev/null
+++ b/android-app/app/src/main/res/layout/fragment_forecast.xml
@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:orientation="vertical"
+    android:background="?attr/colorSurface">
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:paddingHorizontal="16dp"
+        android:paddingTop="16dp"
+        android:paddingBottom="8dp"
+        android:text="7-Day Forecast"
+        android:textAppearance="?attr/textAppearanceHeadline6"
+        android:textColor="?attr/colorOnSurface" />
+
+    <ProgressBar
+        android:id="@+id/progress"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center"
+        android:visibility="gone" />
+
+    <TextView
+        android:id="@+id/error_text"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:padding="16dp"
+        android:textColor="@color/wind_strong"
+        android:visibility="gone" />
+
+    <androidx.recyclerview.widget.RecyclerView
+        android:id="@+id/forecast_list"
+        android:layout_width="match_parent"
+        android:layout_height="0dp"
+        android:layout_weight="1"
+        android:clipToPadding="false"
+        android:paddingBottom="8dp" />
+
+</LinearLayout>
diff --git a/android-app/app/src/main/res/layout/fragment_map.xml b/android-app/app/src/main/res/layout/fragment_map.xml
new file mode 100644
index 0000000..e5b86b7
--- /dev/null
+++ b/android-app/app/src/main/res/layout/fragment_map.xml
@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+
+    <org.maplibre.android.maps.MapView
+        android:id="@+id/map_view"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        app:maplibre_cameraTargetLat="37.0"
+        app:maplibre_cameraTargetLng="-122.0"
+        app:maplibre_cameraZoom="5.0" />
+
+    <!-- Loading / error overlay -->
+    <TextView
+        android:id="@+id/status_text"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="top|center_horizontal"
+        android:layout_marginTop="16dp"
+        android:background="#AA000000"
+        android:paddingHorizontal="12dp"
+        android:paddingVertical="4dp"
+        android:textColor="#FFFFFF"
+        android:textSize="14sp"
+        android:visibility="gone" />
+
+</FrameLayout>
diff --git a/android-app/app/src/main/res/layout/item_forecast.xml b/android-app/app/src/main/res/layout/item_forecast.xml
new file mode 100644
index 0000000..473661a
--- /dev/null
+++ b/android-app/app/src/main/res/layout/item_forecast.xml
@@ -0,0 +1,59 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:orientation="horizontal"
+    android:paddingHorizontal="16dp"
+    android:paddingVertical="12dp"
+    android:gravity="center_vertical">
+
+    <!-- Time -->
+    <TextView
+        android:id="@+id/tv_time"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_weight="2"
+        android:textAppearance="?attr/textAppearanceBody2"
+        android:textColor="?attr/colorOnSurface" />
+
+    <!-- Weather description -->
+    <TextView
+        android:id="@+id/tv_description"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_weight="3"
+        android:textAppearance="?attr/textAppearanceBody2"
+        android:textColor="?attr/colorOnSurface" />
+
+    <!-- Wind -->
+    <TextView
+        android:id="@+id/tv_wind"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_weight="2"
+        android:gravity="end"
+        android:textAppearance="?attr/textAppearanceBody2"
+        android:textColor="?attr/colorOnSurface" />
+
+    <!-- Temperature -->
+    <TextView
+        android:id="@+id/tv_temp"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_weight="1.5"
+        android:gravity="end"
+        android:textAppearance="?attr/textAppearanceBody2"
+        android:textColor="?attr/colorOnSurface" />
+
+    <!-- Precip probability -->
+    <TextView
+        android:id="@+id/tv_precip"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_weight="1.5"
+        android:gravity="end"
+        android:textAppearance="?attr/textAppearanceBody2"
+        android:textColor="@color/primary" />
+
+</LinearLayout>