chore: extract reusable uv_setup composite action (#7262)

Extract a composite GitHub Action for Python + uv setup, replacing 12
scattered `astral-sh/setup-uv@v7` calls with a single reusable
`uv_setup` action that scopes cache dependency globs per library. Also
tightens issue template language and fixes a broken expression in the
release-test workflow.

## Changes

- Add `.github/actions/uv_setup/action.yml` — composite action wrapping
`astral-sh/setup-uv@v7` with a `working-directory` input that scopes
`cache-dependency-glob` to `<dir>/pyproject.toml`, `<dir>/uv.lock`, and
`<dir>/requirements*.txt`
- Migrate all workflow files (`_test.yml`, `_lint.yml`,
`_test_langgraph.yml`, `_integration_test.yml`, `baseline.yml`,
`bench.yml`, `ci.yml`, `release.yml`, `_test_release.yml`,
`uv_lock_ugprade.yml`) from inline `astral-sh/setup-uv@v7` to
`./.github/actions/uv_setup`, passing library-specific
`working-directory` for cache scoping
- Fix typo in `_test_release.yml` step name: `$${ env.PYTHON_VERSION }}`
→ `${{ env.PYTHON_VERSION }}`
- Disable uv cache for the release smoke-test job (`enable-cache:
false`) since it installs from PyPI, not the local lockfile
- Update `config.yml` API reference URL to point to `/python/langgraph/`
instead of `/python/`
- Tighten `privileged.yml` — shorter description, add English language
policy link, add "do not begin work unless assigned" notice

.github/workflows/_test_langgraph.yml

@@ -25,11 +25,11 @@ jobs:
     steps:
       - uses: actions/checkout@v6
       - name: Set up Python ${{ matrix.python-version }}
-        uses: astral-sh/setup-uv@v7
+        uses: ./.github/actions/uv_setup
         with:
           python-version: ${{ matrix.python-version }}
-          enable-cache: true
           cache-suffix: "test-langgraph"
+          working-directory: libs/langgraph
       - name: Login to Docker Hub
         uses: docker/login-action@v4
         if: ${{ !github.event.pull_request.head.repo.fork }}