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_analyzer.py

@@ -1,9 +1,11 @@
 """Tests for the high-level company analyzer orchestration."""
 
+from unittest.mock import MagicMock, Mock
+
 import pytest
-from unittest.mock import Mock, patch, call, MagicMock
+
 from SPARC.analyzer import CompanyAnalyzer
-from SPARC.types import Patent, Patents, CompanyAnalysisResult, BatchAnalysisResult
+from SPARC.types import BatchAnalysisResult, Patent, Patents
 
 
 @pytest.fixture(autouse=True)
@@ -24,7 +26,7 @@ class TestCompanyAnalyzer:
         """Test analyzer initialization with API key."""
         mock_llm = mocker.patch("SPARC.analyzer.LLMAnalyzer")
 
-        analyzer = CompanyAnalyzer(openrouter_api_key="test-key")
+        _analyzer = CompanyAnalyzer(openrouter_api_key="test-key")  # noqa: F841
 
         mock_llm.assert_called_once_with(api_key="test-key")
 

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

tests/test_llm.py

@@ -1,7 +1,9 @@
 """Tests for LLM analysis functionality."""
 
+from unittest.mock import Mock
+
 import pytest
-from unittest.mock import Mock, MagicMock, patch
+
 from SPARC.llm import LLMAnalyzer
 
 

tests/test_serp_api.py

@@ -1,9 +1,8 @@
 """Tests for SERP API patent retrieval and parsing functionality."""
 
-import os
-import pytest
-from unittest.mock import patch, Mock
 from datetime import datetime, timedelta
+from unittest.mock import Mock
+
 from SPARC.serp_api import SERP
 from SPARC.types import Patent