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/evidence.py

@@ -1,5 +1,6 @@
 import uuid
-from sqlalchemy import Column, String, Text, DateTime, ForeignKey, Enum, func
+
+from sqlalchemy import Column, DateTime, Enum, ForeignKey, String, Text, func
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import relationship
 
@@ -10,10 +11,10 @@ from app.models.enums import TeamSide
 class Evidence(Base):
     """
     Evidence model for storing file metadata associated with tests.
-    
+
     Files are stored in MinIO, and this model tracks the file location,
     integrity hash, and upload metadata.
-    
+
     The ``team`` field distinguishes whether this evidence was uploaded by
     Red Team (attack evidence) or Blue Team (detection evidence).
     """