Add flake update scheduled workflow

Author: chreekat

.github/workflows/update-flake.yml

@@ -0,0 +1,26 @@
+name: Update flake inputs
+
+on:
+  schedule:
+    - cron: "0 0 * * 0" # Weekly on Sunday at midnight
+  workflow_dispatch:
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: cachix/install-nix-action@v31
+
+      - name: Update flake inputs
+        run: nix flake update
+
+      - name: Create PR
+        uses: peter-evans/create-pull-request@v7
+        with:
+          commit-message: "nix flake update"
+          title: "nix flake update"
+          body: Automated flake input updates.
+          branch: automated/flake-update
+          delete-branch: true