Add cron workflow to update driverless printer list

.github/workflows/update-driverless.yml

@@ -0,0 +1,72 @@
+name: Update driverless printer list
+
+on:
+  schedule:
+    # Monthly, 1st of the month at 06:00 UTC
+    - cron: '0 6 1 * *'
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+# A manual run must not overlap a scheduled one mid-PR.
+concurrency:
+  group: "update-driverless"
+  cancel-in-progress: false
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      # The script must run from driverless/: it reads ./convert-airprint.py and
+      # ./add-ippeve-only.py and writes ../public/assets/json/driverless.json.
+      - name: Update printer list
+        working-directory: driverless
+        run: ./update-printer-list.sh
+
+      # Guard against an empty/garbled list slipping through (#223). The script
+      # has no `set -e`, so a failed upstream fetch can still exit 0 with a
+      # truncated file; fail the run before any PR is opened.
+      - name: Validate updated list
+        run: |
+          python3 - <<'PY'
+          import json, sys
+          try:
+              with open('public/assets/json/driverless.json') as f:
+                  data = json.load(f)
+          except Exception as e:
+              print(f'::error::driverless.json is not valid JSON ({e}). Aborting.')
+              sys.exit(1)
+          if not isinstance(data, list):
+              print(f'::error::driverless.json must be a JSON array, got {type(data).__name__}. Aborting.')
+              sys.exit(1)
+          count = 0
+          for p in data:
+              if not isinstance(p, dict) or 'model' not in p:
+                  print(f'::error::driverless.json contains a malformed entry: {p!r}. Aborting.')
+                  sys.exit(1)
+              if p['model'] != '_dummy_':
+                  count += 1
+          print(f'Driverless printers: {count}')
+          if count < 5000:
+              print(f'::error::driverless.json has only {count} printers; expected thousands. Aborting.')
+              sys.exit(1)
+          PY
+
+      - name: Create Pull Request
+        uses: peter-evans/create-pull-request@v8
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          add-paths: public/assets/json/driverless.json
+          branch: update-driverless-list
+          delete-branch: true
+          commit-message: "Update driverless printer list"
+          title: "Update driverless printer list"
+          body: |
+            Automated monthly update of the driverless (AirPrint + IPP Everywhere)
+            printer list, generated by `driverless/update-printer-list.sh`.