fix: add UV env vars to mypy full type checking step

The mypy step runs uv commands directly and needs access to
UV_EXTRA_INDEX_URL and UV_INDEX_STRATEGY to resolve RC dependencies
from test.pypi on release branches.

.github/workflows/pre-commit.yml

@@ -147,6 +147,9 @@ jobs:
           echo "MYPY_CMD=$MYPY_CMD" >> $GITHUB_ENV
 
       - name: Run mypy (full type checking)
+        env:
+          UV_EXTRA_INDEX_URL: ${{ steps.client-config.outputs.uv-extra-index-url }}
+          UV_INDEX_STRATEGY: ${{ steps.client-config.outputs.uv-extra-index-url && 'unsafe-best-match' || '' }}
         run: |
           set +e
           output=$($MYPY_CMD 2>&1)