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/routers/auth.py

@@ -11,11 +11,10 @@ import os
 
 from fastapi import APIRouter, Cookie, Depends, Request, Response
 from fastapi.security import OAuth2PasswordRequestForm
+from jose import JWTError, jwt
 from sqlalchemy.orm import Session
 
-from jose import jwt, JWTError
-
-from app.auth import create_access_token, blacklist_token, verify_password
+from app.auth import blacklist_token, create_access_token, verify_password
 from app.config import settings
 from app.database import get_db
 from app.dependencies.auth import get_current_user
@@ -24,13 +23,15 @@ from app.domain.unit_of_work import UnitOfWork
 from app.limiter import limiter
 from app.middleware.request_context import resolve_client_ip
 from app.models.user import User
-from app.services.auth_service import (
-    _DUMMY_HASH,
-    change_password as auth_change_password,
-)
-from app.services.audit_service import log_action
 from app.schemas.auth import TokenResponse, UserOut
 from app.schemas.user import PasswordChange
+from app.services.audit_service import log_action
+from app.services.auth_service import (
+    _DUMMY_HASH,
+)
+from app.services.auth_service import (
+    change_password as auth_change_password,
+)
 
 router = APIRouter(prefix="/auth", tags=["auth"])