ci: add pytest and ruff linting to CI, fix all lint errors

- Add test job to build.yaml that runs pytest and ruff before building images
- Add standalone test.yaml workflow for PRs
- Add ruff.toml with E/F/I rules configured
- Fix all ruff lint errors: sort imports, remove unused imports, fix re-exports
- Build jobs now depend on test job passing (needs: test)

Closes leeworks-agents/SPARC#18
Closes leeworks-agents/SPARC#19

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

tests/test_api.py

@@ -1,12 +1,13 @@
 """Tests for FastAPI web service endpoints."""
 
-import pytest
 from datetime import datetime
-from unittest.mock import Mock, patch
+from unittest.mock import Mock
+
+import pytest
 from fastapi.testclient import TestClient
 
 from SPARC.api import app
-from SPARC.types import CompanyAnalysisResult, BatchAnalysisResult
+from SPARC.types import BatchAnalysisResult, CompanyAnalysisResult
 
 
 @pytest.fixture