chore: Add VS Code settings for pytest test discovery

- Configure pytest args to point to src/tests directory
- Enable pytest and disable unittest in VS Code
- Set correct Python interpreter path to .venv
- Fix VS Code test discovery issue

🤖 Generated with [Claude Code](https://claude.ai/code)

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

.vscode/settings.json

@@ -0,0 +1,8 @@
+{
+  "python.testing.pytestEnabled": true,
+  "python.testing.unittestEnabled": false,
+  "python.testing.pytestArgs": [
+    "src/tests"
+  ],
+  "python.defaultInterpreterPath": "./.venv/bin/python"
+}