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/release.yml

@@ -8,7 +8,7 @@ on:
 jobs:
   release:
     if: ${{ !contains(github.event.head_commit.message, '[skip ci]') }}
-    runs-on: ubuntu-latest
+    runs-on: python-repositories-ci
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -22,19 +22,12 @@ jobs:
           COMMIT_MSG: ${{ github.event.head_commit.message }}
         run: scripts/ci/parse-merge-commit.sh "$COMMIT_MSG"
 
-      - name: Set up Python
-        if: steps.meta.outputs.bump != 'skip'
-        uses: actions/setup-python@v5
-        with:
-          python-version-file: .python-version
-
-      - name: Install uv
-        if: steps.meta.outputs.bump != 'skip'
-        run: pip install uv
-
       - name: Bump version
         if: steps.meta.outputs.bump != 'skip'
         id: bump
+        env:
+          UV_INDEX_GITEA_USERNAME: ci-bot
+          UV_INDEX_GITEA_PASSWORD: ${{ secrets.CI_RUNNER_TOKEN }}
         run: scripts/ci/bump-version.sh "${{ steps.meta.outputs.bump }}"
 
       - name: Generate release notes