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!

backend/app/schemas/__init__.py

@@ -1,32 +1,28 @@
 """Pydantic schemas — re-exported for convenient imports."""
 
 from app.schemas.auth import LoginRequest, TokenResponse, UserOut
-
+from app.schemas.evidence import EvidenceOut, EvidenceUpload
 from app.schemas.technique import (
     TechniqueCreate,
     TechniqueOut,
     TechniqueSummary,
     TechniqueUpdate,
 )
-
 from app.schemas.test import (
+    TestBlueUpdate,
+    TestBlueValidate,
     TestCreate,
     TestOut,
+    TestRedUpdate,
+    TestRedValidate,
     TestUpdate,
     TestValidate,
-    TestRedUpdate,
-    TestBlueUpdate,
-    TestRedValidate,
-    TestBlueValidate,
 )
-
-from app.schemas.evidence import EvidenceOut, EvidenceUpload
-
 from app.schemas.test_template import (
-    TestTemplateOut,
     TestTemplateCreate,
-    TestTemplateSummary,
     TestTemplateInstantiate,
+    TestTemplateOut,
+    TestTemplateSummary,
 )
 
 __all__ = [