fix: CI failures — update workflow for uv migration, fix lint and format

- Switch CI install step from `pip install -r requirements.txt` to
  `pip install -e ".[dev]"` since requirements.txt was removed
- Add noqa: E402 to intentionally-late imports in conftest.py
  (HOME must be isolated before mempalace imports)
- Remove unused KnowledgeGraph import in test_knowledge_graph.py
- Apply ruff formatting to test files

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.python-version }}
-      - run: pip install -r requirements.txt pytest
+      - run: pip install -e ".[dev]"
       - run: python -m pytest tests/ -v
 
   lint: