CI: add weeklyUpdate workflow

.github/workflows/weeklyUpdate.yml

@@ -0,0 +1,58 @@
+name: Weekly Flake Update
+
+on:
+  schedule:
+    - cron: "0 3 * * 1"  # every Monday at 03:00 UTC
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  flake_update:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: DeterminateSystems/nix-installer-action@v12
+
+      - name: Set branch name (date)
+        id: vars
+        run: |
+          echo "branch=flake-update/$(date +%Y-%m-%d)" >> $GITHUB_OUTPUT
+
+      - name: Create update branch
+        run: |
+          git checkout -B ${{ steps.vars.outputs.branch }}
+
+      - name: Update flake inputs
+        run: |
+          nix flake update
+
+      - name: Commit changes
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git add flake.lock
+          git commit -m "chore: weekly flake update" || echo "No changes to commit"
+
+      - name: Push branch
+        run: |
+          git push origin ${{ steps.vars.outputs.branch }} --force
+
+      - name: Install GitHub CLI
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y gh
+
+      - name: Create Pull Request
+        run: |
+          gh pr create \
+            --base main \
+            --head ${{ steps.vars.outputs.branch }} \
+            --title "[Automated] Weekly flake update $(date +%Y-%m-%d)" \
+            --body "Automated weekly update of flake inputs for $(date +%Y-%m-%d)."
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}