CI: Add debug builds to ease contributing and review

.github/workflows/build.yml

@@ -0,0 +1,43 @@
+name: Build Debug
+
+permissions:
+  contents: read
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+  workflow_dispatch:
+
+jobs:
+  build:
+    name: Build Debug
+    runs-on: ubuntu-latest
+    steps:
+      - name: Code checkout
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+
+      - name: Set up Flutter
+        uses: subosito/flutter-action@1a449444c387b1966244ae4d4f8c696479add0b2 # v2.23.0
+        with:
+          cache: true
+          channel: stable
+          flutter-version-file: .fvmrc
+
+      - name: Fetch dependencies
+        run: |
+          set -eu
+          flutter config --no-analytics
+          flutter pub get
+
+      - name: Build app
+        run: |
+          set -eu
+          flutter build apk --debug --no-shrink
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
+        with:
+          name: piwigo-app
+          path: build/app/outputs/flutter-apk/app-debug.apk