feat: comprehensive test infrastructure improvements

- Fix unit test imports: add env setup in conftest.py before module imports
- Add 24 new auth router tests (RBAC, preferences, password validation)
- Add 16 new tests for litellm and chat_summary routers
- Apply black formatting and ruff linting across codebase
- Add pre-commit hooks configuration (black, ruff, file checks)
- Increase CI coverage threshold from 40% to 50%

Test Results:
- 206 tests passing (91 unit + 115 integration)
- Coverage: 58.79% on core modules
- auth.py: 57% → 85%, litellm.py: 23% → 87%, chat_summary.py: 41% → 100%
- auth_service: 96.51%, config: 100%, rbac: 93.48%

dashboard/backend/services/email_service.py

@@ -1,11 +1,12 @@
 """
 Email notification service for OPC
 """
+
+import logging
 import os
 import smtplib
-from email.mime.text import MIMEText
 from email.mime.multipart import MIMEMultipart
-import logging
+from email.mime.text import MIMEText
 
 logger = logging.getLogger(__name__)
 
@@ -90,7 +91,9 @@ async def send_agent_approval_email(agent_name: str, task: dict, reasoning: str,
     """Send email for agent approval request"""
     subject = f"Agent Approval Required: {agent_name}"
 
-    actions_text = "\n".join([f"- {action.get('type')}: {action.get('title', action.get('message', 'N/A'))}" for action in actions])
+    actions_text = "\n".join(
+        [f"- {action.get('type')}: {action.get('title', action.get('message', 'N/A'))}" for action in actions]
+    )
 
     body = f"""Agent approval required: