Add gitea action for updating flake

.gitea/workflows/update-flake.yaml

@@ -0,0 +1,41 @@
+name: Update Nix Flake
+
+on:
+  schedule:
+    - cron: "30 0 * * *" # daily run
+  workflow_dispatch: {}
+
+jobs:
+  update-flake:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          token: "${{ secrets.GH_TOKEN }}"
+          fetch-depth: 0
+          ref: flake-updates
+
+      - name: Fetch latest changes and reset branch
+        run: |
+          git fetch origin master
+          git reset --hard origin/master
+
+      - name: Set up Nix
+        uses: cachix/install-nix-action@v31
+
+      - name: Update Flake
+        run: nix flake update
+
+      - name: Commit and push changes
+        shell: bash
+        run: |
+          git config user.name "Gitea Actions"
+          git config user.email "actions@gitea.local"
+          git add flake.lock
+          if git diff --cached --quiet; then
+            echo "No changes to commit."
+          else
+            git commit -m "Update flake.lock $(date -I)"
+            git push origin flake-updates
+          fi