ci(android): add GitHub Actions workflows for debug APK builds

Adds two workflows:
- build-fdroid-debug.yml: builds fdroidDebug variant (no Firebase)
- build-play-debug.yml: builds playDebug variant (with Firebase)

Both run on push/PR to main and upload APK artifacts.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/build-fdroid-debug.yml

@@ -0,0 +1,46 @@
+name: Build F-Droid Debug APK
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'app/**'
+      - '.github/workflows/build-fdroid-debug.yml'
+  pull_request:
+    branches: [main]
+    paths:
+      - 'app/**'
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Set up JDK 21
+        uses: actions/setup-java@v4
+        with:
+          java-version: '21'
+          distribution: 'temurin'
+
+      - name: Cache Gradle
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: ${{ runner.os }}-gradle-
+
+      - name: Build F-Droid Debug APK
+        run: ./gradlew :app:assembleFdroidDebug --no-daemon
+
+      - name: Upload APK
+        uses: actions/upload-artifact@v4
+        with:
+          name: centralcloud-oncall-fdroid-debug
+          path: app/build/outputs/apk/fdroid/debug/*.apk

.github/workflows/build-play-debug.yml

@@ -0,0 +1,46 @@
+name: Build Play Debug APK
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'app/**'
+      - '.github/workflows/build-play-debug.yml'
+  pull_request:
+    branches: [main]
+    paths:
+      - 'app/**'
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Set up JDK 21
+        uses: actions/setup-java@v4
+        with:
+          java-version: '21'
+          distribution: 'temurin'
+
+      - name: Cache Gradle
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: ${{ runner.os }}-gradle-
+
+      - name: Build Play Debug APK
+        run: ./gradlew :app:assemblePlayDebug --no-daemon
+
+      - name: Upload APK
+        uses: actions/upload-artifact@v4
+        with:
+          name: centralcloud-oncall-play-debug
+          path: app/build/outputs/apk/play/debug/*.apk