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>

1 files changed, 21 insertions, 0 deletions

diff --git a/android-app/app/src/main/res/drawable/ic_wind_arrow.xml b/android-app/app/src/main/res/drawable/ic_wind_arrow.xml
new file mode 100644
index 0000000..110f1b3
--- /dev/null
+++ b/android-app/app/src/main/res/drawable/ic_wind_arrow.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Wind-direction arrow pointing UP (north).
+  MapLibre rotates the icon to match wind direction via icon-rotate expression.
+-->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+
+    <!-- Arrowhead pointing up -->
+    <path
+        android:fillColor="#FFFFFF"
+        android:pathData="M12,2 L18,14 L12,11 L6,14 Z" />
+    <!-- Shaft -->
+    <path
+        android:fillColor="#FFFFFF"
+        android:pathData="M11,11 L11,22 L13,22 L13,11 Z" />
+
+</vector>