Add nightly CI base image and migrate workflows to python-repositories-ci.

Pre-build Python, uv, and locked deps in a Gitea container image so daily jobs skip repeated bootstrap; document runner registry auth and ci-bot credentials.

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitea/workflows/ci-image.yml

@@ -0,0 +1,52 @@
+# Build and publish the per-repo CI base image to the Gitea container registry.
+
+name: Build CI Image
+
+on:
+  schedule:
+    - cron: "0 2 * * *"
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+    paths:
+      - pyproject.toml
+      - uv.lock
+      - docker/ci/**
+
+env:
+  REGISTRY: gitea.lille-vemmelund.dk
+  REGISTRY_USER: ci-bot
+  IMAGE: gitea.lille-vemmelund.dk/brian/python-repositories-ci
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Log in to Gitea container registry
+        env:
+          CI_RUNNER_TOKEN: ${{ secrets.CI_RUNNER_TOKEN }}
+        run: |
+          echo "$CI_RUNNER_TOKEN" | docker login "$REGISTRY" -u "$REGISTRY_USER" --password-stdin
+
+      - name: Build CI image
+        env:
+          CI_RUNNER_TOKEN: ${{ secrets.CI_RUNNER_TOKEN }}
+        run: |
+          echo "$CI_RUNNER_TOKEN" > /tmp/uv_token
+          docker build -f docker/ci/Dockerfile \
+            --secret id=uv_token,src=/tmp/uv_token \
+            -t "${IMAGE}:latest" \
+            .
+          rm -f /tmp/uv_token
+
+      - name: Tag and push CI image
+        run: |
+          STAMP="$(date -u +%Y%m%d%H%M)"
+          docker tag "${IMAGE}:latest" "${IMAGE}:${STAMP}"
+          docker push "${IMAGE}:latest"
+          docker push "${IMAGE}:${STAMP}"
+          echo "Pushed ${IMAGE}:latest and ${IMAGE}:${STAMP}"