Fix all 33 ruff linting errors causing CI failures

- Remove unused imports (F401) across 17 files
- Fix f-strings without placeholders (F541) in 3 files
- Add noqa: E712 to SQLAlchemy == True comparisons (valid ORM pattern)
- Preserve alembic side-effect import with noqa: F401

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
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backend/tests/unit/test_gmail_service.py

@@ -3,7 +3,7 @@ Unit tests for Gmail service module.
 """
 
 import pytest
-from unittest.mock import MagicMock, patch, AsyncMock
+from unittest.mock import MagicMock
 from app.services.gmail_service import GmailService, GmailInjectionError, GMAIL_SCOPES
 
 

backend/tests/unit/test_provider_presets.py

@@ -2,7 +2,6 @@
 Unit tests for provider presets and mail server auto-detection.
 """
 
-import pytest
 from app.services.mail_processor import MailServerAutoDetect