update and add build action

.github/workflows/flatpak.yml

@@ -0,0 +1,48 @@
+name: Flatpak Build
+
+on:
+  schedule:
+    - cron: '0 2 * * *'
+  workflow_dispatch:
+
+jobs:
+  flatpak:
+    name: "Build Flatpak"
+    runs-on: ubuntu-latest
+    container:
+      image: ghcr.io/flathub-infra/flatpak-github-actions:freedesktop-24.08
+      options: --privileged
+    
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Build Flatpak
+        uses: flatpak/flatpak-github-actions/flatpak-builder@v6
+        with:
+          bundle: org.sdrpp.App.flatpak
+          manifest-path: org.sdrpp.App.yaml
+          cache-key: flatpak-builder-${{ github.sha }}
+
+      - name: Get current date
+        id: date
+        run: echo "date=$(date +'%Y-%m-%d')" >> $GITHUB_OUTPUT
+
+      - name: Delete existing release
+        uses: dev-drprasad/delete-tag-and-release@v1.1
+        with:
+          tag_name: nightly
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          delete_release: true
+        continue-on-error: true
+
+      - name: Upload Release
+        uses: softprops/action-gh-release@v2
+        with:
+          tag_name: nightly
+          name: "Nightly Build (${{ steps.date.outputs.date }})"
+          files: org.sdrpp.App.flatpak
+          body: |
+            **Build Date:** ${{ steps.date.outputs.date }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}