ci(app): Flutter CI-джоба + сборка Linux/Windows

analyze+test и flutter build linux/windows в отдельных джобах по образцу
backend. Линуксовая сборка требует libsecret-1-dev/pkg-config (apt) и
подавления -Werror=deprecated-literal-operator в CMake — flutter_secure_storage_linux
вендорит старый nlohmann/json.hpp, который на новых компиляторах иначе
не собирается.

.github/workflows/ci.yml

@@ -40,3 +40,50 @@ jobs:
         run: |
           uv run fintracker openapi /tmp/openapi.json
           diff -u ../openapi/openapi.json /tmp/openapi.json
+
+  app:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: app
+    steps:
+      - uses: actions/checkout@v4
+      - uses: subosito/flutter-action@v2
+        with:
+          flutter-version: "3.47.4"
+          channel: stable
+      - run: flutter pub get
+      - run: flutter analyze
+      - run: flutter test
+
+  app-build-linux:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: app
+    steps:
+      - uses: actions/checkout@v4
+      - uses: subosito/flutter-action@v2
+        with:
+          flutter-version: "3.47.4"
+          channel: stable
+      - name: install Linux desktop build dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y clang cmake ninja-build pkg-config libgtk-3-dev libsecret-1-dev
+      - run: flutter pub get
+      - run: flutter build linux --release
+
+  app-build-windows:
+    runs-on: windows-latest
+    defaults:
+      run:
+        working-directory: app
+    steps:
+      - uses: actions/checkout@v4
+      - uses: subosito/flutter-action@v2
+        with:
+          flutter-version: "3.47.4"
+          channel: stable
+      - run: flutter pub get
+      - run: flutter build windows --release