refactor(pep8): enforce full PEP8 compliance across backend Python codebase

- ruff.toml: select E/W/F/I/N rules, line-length=120, drop legacy ignores
- Auto-fix: sort 82 import blocks (isort), remove 29 unused imports,
  strip 6 trailing-whitespace blank lines in docstrings
- main.py: move setup_logging and settings imports to top (E402)
- errors.py: noqa N818 on DDD exception names (96 call sites, safe)
- intel_service.py: noqa N817 for universal ET alias
- atomic/elastic/sigma import services: move _MAX_UNCOMPRESSED_SIZE and
  _MAX_ENTRIES to module level (N806)
- compliance_import_service.py: move SAMPLE_CONTROLS / CIS_CONTROLS to
  module level; wrap long description strings (N806 + E501)
- snapshot_service.py: move STATUS_ORDER dict to module level (N806)
- sigma_import_service.py: remove dead dedup_key expression (F841)
- threat_actor_import_service.py: remove dead stix_to_actor expression (F841)
- data_source.py, seed_demo.py, campaign_scheduler_service.py,
  lolbas_import_service.py: wrap lines exceeding 120 chars (E501)
- d3fend_import_service.py: per-file E501 ignore (data file with long strings)

All 439 unit tests pass. ruff check app/ → All checks passed!

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/services/scoring_service.py

@@ -10,19 +10,18 @@ never produce N+1 traffic.
 """
 
 from datetime import datetime, timedelta, timezone
-from typing import Optional
 
 from sqlalchemy import case, func
 from sqlalchemy.orm import Session
 
 from app.domain.errors import EntityNotFoundError
+from app.models.defensive_technique import DefensiveTechniqueMapping
+from app.models.detection_rule import DetectionRule
+from app.models.enums import TestResult, TestState
 from app.models.technique import Technique
 from app.models.test import Test
-from app.models.detection_rule import DetectionRule
 from app.models.test_detection_result import TestDetectionResult
-from app.models.defensive_technique import DefensiveTechniqueMapping
 from app.models.threat_actor import ThreatActor, ThreatActorTechnique
-from app.models.enums import TestState, TestResult
 from app.services.scoring_config_service import get_scoring_weights
 
 _SEVERITY_FACTORS: dict[str, float] = {
@@ -659,7 +658,6 @@ def get_score_history(db: Session, period: str = "90d") -> list:
     computing scores based on test dates within time windows.
     Returns a list of weekly data points.
     """
-    from app.models.audit import AuditLog
 
     now = datetime.utcnow()
     if period == "30d":