ci: switch runner from astral-uv to ubuntu-latest

Replaces the self-hosted astral-uv runner (which had uv
pre-installed) with the standard GitHub-hosted ubuntu-latest.
Adds back the astral-sh/setup-uv step that was omitted in the
self-hosted case.

The astral-uv runner was timing out / unreachable from the
GitHub Actions side; ubuntu-latest is universally available.

Trade-off: ubuntu-latest runners start fresh each run (~30s cold
start) and the setup-uv step takes a few seconds to download uv,
versus a self-hosted runner that boots in <1s with uv ready. For
a single CI job that runs on tag push only, the extra ~10s is
not a problem.

Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/build.yml

@@ -11,20 +11,25 @@ on:
 jobs:
   ci:
     name: CI
-    # `astral-uv` is a self-hosted runner with uv pre-installed, so we can
-    # skip the setup-uv step entirely. pyproject.toml's
-    # [tool.hatch.build.hooks.jupyter-builder] handles jlpm install +
-    # jlpm build:prod before wheel assembly.
-    runs-on: astral-uv
+    # Standard GitHub-hosted ubuntu runner. uv is installed via the
+    # astral-sh/setup-uv action (one extra step vs. using a self-hosted
+    # runner with uv pre-installed, but matches what GitHub-hosted CI
+    # provides out of the box).
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Set up uv
+        uses: astral-sh/setup-uv@v6
+        with:
+          enable-cache: true
+
       - name: Build package
         env:
           # Use the Tsinghua PyPI mirror for build-environment resolution;
-          # the self-hosted runner is in China and the default pypi.org is
-          # too slow / unreliable for build dependency install.
+          # the runner is in China and the default pypi.org is too slow
+          # / unreliable for build dependency install.
           UV_DEFAULT_INDEX: "https://pypi.tuna.tsinghua.edu.cn/simple/"
         run: uv build