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/routers/test_templates.py

@@ -40,13 +40,21 @@ from app.schemas.test_template import (
 from app.services.audit_service import log_action
 from app.services.test_template_service import (
     bulk_activate,
-    create_template as create_template_svc,
     get_template_or_raise,
     get_template_stats,
-    get_templates_by_technique as templates_by_technique,
     list_templates,
     soft_delete_template,
+)
+from app.services.test_template_service import (
+    create_template as create_template_svc,
+)
+from app.services.test_template_service import (
+    get_templates_by_technique as templates_by_technique,
+)
+from app.services.test_template_service import (
     toggle_template_active as toggle_template_active_svc,
+)
+from app.services.test_template_service import (
     update_template as update_template_svc,
 )