test(webui): add unit tests for ConfigSchemaGenerator

- Test field descriptions from field_docs
- Test json_schema_extra merging
- Test Pydantic constraints mapping
- Test nested model schema handling
- Test fields without extra metadata

All 5 tests passing. Completes Task 7 of webui-config-visualization-refactor plan.

pytests/conftest.py

@@ -0,0 +1,6 @@
+import sys
+from pathlib import Path
+
+# Add project root to Python path so src imports work
+project_root = Path(__file__).parent.parent.absolute()
+sys.path.insert(0, str(project_root))