feat: android webview app + APK build script + CI artifact

Android app (WebView wrapper):
- Wraps the public household sharing URL in a native Android app
- Swipe-to-refresh, error handling, back navigation, settings dialog
- User enters their household's public URL on first launch
- Material Design with toolbar, progress indicator

Build tooling:
- build-apk.sh: one-command APK build (auto-installs Java, SDK, Gradle)
- .gitignore updated for Android build artifacts

CI (.gitea/workflows/ci.yml):
- New 'build-android' job (needs test-and-package)
- Installs Android SDK + Java 17, builds debug APK
- Uploads APK as 'meal-tracker-apk' artifact

.gitea/workflows/ci.yml

@@ -38,3 +38,56 @@ jobs:
         with:
           name: meal-tracker
           path: meal-tracker.zip
+
+  build-android:
+    runs-on: ubuntu-latest
+    needs: test-and-package
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Setup Java 17
+        uses: actions/setup-java@v3
+        with:
+          distribution: temurin
+          java-version: "17"
+
+      - name: Build APK
+        run: |
+          export ANDROID_SDK_ROOT="$HOME/android-sdk"
+          mkdir -p "$ANDROID_SDK_ROOT"
+
+          # Download Android command-line tools
+          wget -q https://dl.google.com/android/repository/commandlinetools-linux-11076708_latest.zip \
+            -O /tmp/cmdline-tools.zip
+          unzip -qo /tmp/cmdline-tools.zip -d /tmp/cmdline-tools-tmp
+          mkdir -p "$ANDROID_SDK_ROOT/cmdline-tools"
+          mv /tmp/cmdline-tools-tmp/cmdline-tools "$ANDROID_SDK_ROOT/cmdline-tools/latest"
+
+          # Accept licenses and install SDK packages
+          yes | "$ANDROID_SDK_ROOT/cmdline-tools/latest/bin/sdkmanager" --licenses > /dev/null 2>&1
+          "$ANDROID_SDK_ROOT/cmdline-tools/latest/bin/sdkmanager" \
+            "platform-tools" \
+            "build-tools;34.0.0" \
+            "platforms;android-34" > /dev/null 2>&1
+
+          # Create local.properties
+          echo "sdk.dir=$ANDROID_SDK_ROOT" > android/local.properties
+
+          # Download Gradle
+          wget -q https://services.gradle.org/distributions/gradle-8.7-bin.zip -O /tmp/gradle.zip
+          mkdir -p android/.gradle-home
+          unzip -qo /tmp/gradle.zip -d android/.gradle-home
+
+          # Generate wrapper
+          cd android
+          .gradle-home/gradle-8.7/bin/gradle wrapper --gradle-version 8.7 --no-daemon
+
+          # Build
+          ./gradlew assembleDebug --no-daemon
+
+      - name: Upload APK artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: meal-tracker-apk
+          path: android/app/build/outputs/apk/debug/*.apk