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/models/__init__.py

@@ -1,26 +1,30 @@
 # Import all models here so Alembic can detect them
-from app.models.user import User
-from app.models.technique import Technique
-from app.models.test import Test
-from app.models.test_template import TestTemplate
+from app.models.audit import AuditLog
+from app.models.campaign import Campaign, CampaignTest
+from app.models.compliance import (
+    ComplianceControl,
+    ComplianceControlMapping,
+    ComplianceFramework,
+)
+from app.models.coverage_snapshot import CoverageSnapshot, SnapshotTechniqueState
+from app.models.data_source import DataSource
+from app.models.defensive_technique import DefensiveTechnique, DefensiveTechniqueMapping
+from app.models.detection_rule import DetectionRule
+from app.models.enums import TeamSide, TechniqueStatus, TestResult, TestState
 from app.models.evidence import Evidence
 from app.models.intel import IntelItem
-from app.models.audit import AuditLog
-from app.models.notification import Notification
-from app.models.data_source import DataSource
-from app.models.detection_rule import DetectionRule
-from app.models.threat_actor import ThreatActor, ThreatActorTechnique
-from app.models.defensive_technique import DefensiveTechnique, DefensiveTechniqueMapping
-from app.models.test_template_detection_rule import TestTemplateDetectionRule
-from app.models.test_detection_result import TestDetectionResult
-from app.models.campaign import Campaign, CampaignTest
-from app.models.compliance import ComplianceFramework, ComplianceControl, ComplianceControlMapping
-from app.models.coverage_snapshot import CoverageSnapshot, SnapshotTechniqueState
 from app.models.jira_link import JiraLink, JiraLinkEntityType, JiraSyncDirection
-from app.models.worklog import Worklog
+from app.models.notification import Notification
 from app.models.osint_item import OsintItem
 from app.models.scoring_config import ScoringConfig
-from app.models.enums import TechniqueStatus, TestState, TestResult, TeamSide
+from app.models.technique import Technique
+from app.models.test import Test
+from app.models.test_detection_result import TestDetectionResult
+from app.models.test_template import TestTemplate
+from app.models.test_template_detection_rule import TestTemplateDetectionRule
+from app.models.threat_actor import ThreatActor, ThreatActorTechnique
+from app.models.user import User
+from app.models.worklog import Worklog
 
 __all__ = [
     "User", "Technique", "Test", "TestTemplate", "Evidence",