fix(ci): create venv before pip install

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Yuerchu

.github/workflows/ci.yml

@@ -35,7 +35,9 @@ jobs:
         run: uv python install 3.12
 
       - name: Install dependencies
-        run: uv pip install -e ".[dev,fastapi,cache,pgvector]"
+        run: |
+          uv venv
+          uv pip install -e ".[dev,fastapi,cache,pgvector]"
 
       - name: Run basedpyright
         run: uv run basedpyright --level error