🔧 Add PR build check workflow

- Builds debug APKs for pull requests (no signing required)
- Runs unit tests
- Uploads APKs as artifacts (30 days retention)
- Posts build status comment to PR
- No production releases for PRs (only on main merge)
- Gradle cache for faster builds

[skip ci]

.github/workflows/pr-build-check.yml

@@ -0,0 +1,113 @@
+name: PR Build Check
+
+on:
+  pull_request:
+    branches: [ main ]
+    paths:
+      - 'android/**'
+      - '.github/workflows/pr-build-check.yml'
+
+jobs:
+  build:
+    name: Build & Test APK
+    runs-on: ubuntu-latest
+    
+    steps:
+      - name: Code auschecken
+        uses: actions/checkout@v4
+      
+      - name: Java einrichten
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '17'
+      
+      - name: Gradle Cache
+        uses: actions/cache@v3
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: |
+            ${{ runner.os }}-gradle-
+      
+      - name: Version auslesen
+        run: |
+          VERSION_NAME=$(grep "versionName = " android/app/build.gradle.kts | sed 's/.*versionName = "\(.*\)".*/\1/')
+          VERSION_CODE=$(grep "versionCode = " android/app/build.gradle.kts | sed 's/.*versionCode = \([0-9]*\).*/\1/')
+          echo "VERSION_NAME=$VERSION_NAME" >> $GITHUB_ENV
+          echo "VERSION_CODE=$VERSION_CODE" >> $GITHUB_ENV
+          echo "📱 Version: $VERSION_NAME (Code: $VERSION_CODE)"
+      
+      - name: Debug Build erstellen (ohne Signing)
+        run: |
+          cd android
+          ./gradlew assembleStandardDebug assembleFdroidDebug --no-daemon --stacktrace
+      
+      - name: Unit Tests ausfuehren
+        run: |
+          cd android
+          ./gradlew test --no-daemon --stacktrace
+        continue-on-error: true
+      
+      - name: Build-Ergebnis pruefen
+        run: |
+          if [ -f "android/app/build/outputs/apk/standard/debug/app-standard-universal-debug.apk" ]; then
+            echo "✅ Standard Debug APK erfolgreich gebaut"
+            ls -lh android/app/build/outputs/apk/standard/debug/*.apk
+          else
+            echo "❌ Standard Debug APK Build fehlgeschlagen"
+            exit 1
+          fi
+          
+          if [ -f "android/app/build/outputs/apk/fdroid/debug/app-fdroid-universal-debug.apk" ]; then
+            echo "✅ F-Droid Debug APK erfolgreich gebaut"
+            ls -lh android/app/build/outputs/apk/fdroid/debug/*.apk
+          else
+            echo "❌ F-Droid Debug APK Build fehlgeschlagen"
+            exit 1
+          fi
+      
+      - name: Debug APKs hochladen (Artefakte)
+        uses: actions/upload-artifact@v4
+        with:
+          name: debug-apks-pr-${{ github.event.pull_request.number }}
+          path: |
+            android/app/build/outputs/apk/standard/debug/*.apk
+            android/app/build/outputs/apk/fdroid/debug/*.apk
+          retention-days: 30
+      
+      - name: Kommentar zu PR hinzufuegen
+        uses: actions/github-script@v7
+        if: success()
+        with:
+          script: |
+            const fs = require('fs');
+            const standardApk = fs.readdirSync('android/app/build/outputs/apk/standard/debug/')
+              .filter(f => f.endsWith('.apk'));
+            const fdroidApk = fs.readdirSync('android/app/build/outputs/apk/fdroid/debug/')
+              .filter(f => f.endsWith('.apk'));
+            
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: `## ✅ Build erfolgreich!
+              
+**Version:** ${{ env.VERSION_NAME }} (Code: ${{ env.VERSION_CODE }})
+
+### 📦 Debug APKs (Test-Builds)
+
+Die Debug-APKs wurden erfolgreich gebaut und sind als Artefakte verfuegbar:
+
+**Standard Flavor:**
+${standardApk.map(f => '- `' + f + '`').join('\n')}
+
+**F-Droid Flavor:**
+${fdroidApk.map(f => '- `' + f + '`').join('\n')}
+
+> ⚠️ **Hinweis:** Dies sind unsigned Debug-Builds zum Testen. Production Releases werden nur bei Merge auf \`main\` erstellt.
+
+[📥 Download Artefakte](https://github.com/${{ github.repository }}/actions/runs/${{ github.run_id }})`
+            })