refactor(types): add comprehensive type annotations across backend Python codebase

Enable ANN rules in ruff.toml (flake8-annotations) and resolve all 221 violations:

ANN201/ANN202 — return types on 168 public/private functions:
- All 28 FastAPI routers: endpoints annotated with dict/list/specific schema/
  StreamingResponse/FileResponse/JSONResponse as appropriate
- main.py: lifespan→AsyncGenerator[None,None], exception handlers→JSONResponse
- database.py: get_db→Generator[Session,None,None], proxy methods→correct types
- middleware/request_context.py: dispatch→Response with Callable call_next type

ANN001/ANN002/ANN003 — 32 missing argument types:
- seed_demo.py: all db parameters typed as Session
- domain/unit_of_work.py: __aexit__ exc_type/exc_val/exc_tb typed with TracebackType
- services: audit_service user_id→UUID|None, heatmap_service query/model/builder,
  notification_service test→Test, tempo_service test→Test/user→User,
  test_workflow_service test_id→UUID, campaign_crud **fields→object,
  test_crud **fields→object (4 sites)

ANN401 — 16 Any usages resolved:
- Domain entities (campaign/technique/threat_actor/test_entity): replaced Any with
  actual ORM types via TYPE_CHECKING guards to avoid circular imports
- detection_rule_service: test_id/detection_rule_id/evaluator_id→UUID
- score_cache: kept Any with # noqa: ANN401 (genuinely generic cache)
- jira_service/tempo_service: kept Any with # noqa: ANN401 (lazy optional deps)
- d3fend_import_service: _to_str(v: Any) kept with # noqa: ANN401

ANN204/ANN205/ANN206 — special/static/class methods:
- database.py proxy __call__/__getattr__: *args: object/**kwargs: object
- schemas/test.py model_validate: obj→object, **kwargs→object
- sa_technique_repository._int_type→type

All 439 unit tests pass. ruff check app/ → All checks passed!

backend/app/seed_demo.py

@@ -16,6 +16,8 @@ import random
 import uuid
 from datetime import datetime, timedelta
 
+from sqlalchemy.orm import Session
+
 from app.auth import hash_password
 from app.database import SessionLocal
 from app.models.audit import AuditLog
@@ -102,7 +104,7 @@ TEMPLATE_NAMES = [
 # ---------------------------------------------------------------------------
 
 
-def _cleanup_demo_data(db) -> None:
+def _cleanup_demo_data(db: Session) -> None:
     """Remove all previously seeded demo data."""
     # Delete in order to respect FK constraints
     demo_users = db.query(User).filter(User.username.like(f"{DEMO_PREFIX}%")).all()
@@ -154,7 +156,7 @@ def _cleanup_demo_data(db) -> None:
 # ---------------------------------------------------------------------------
 
 
-def _seed_users(db) -> list[User]:
+def _seed_users(db: Session) -> list[User]:
     """Create 5 users per role (25 total)."""
     users = []
     for role in ROLES:
@@ -173,7 +175,7 @@ def _seed_users(db) -> list[User]:
     return users
 
 
-def _seed_technique_statuses(db, count: int = 50) -> list[Technique]:
+def _seed_technique_statuses(db: Session, count: int = 50) -> list[Technique]:
     """Set varied statuses on up to *count* techniques."""
     techniques = db.query(Technique).limit(count).all()
     if not techniques:
@@ -192,7 +194,7 @@ def _seed_technique_statuses(db, count: int = 50) -> list[Technique]:
     return techniques
 
 
-def _seed_tests(db, users: list[User], techniques: list[Technique], count: int = 100) -> list[Test]:
+def _seed_tests(db: Session, users: list[User], techniques: list[Technique], count: int = 100) -> list[Test]:
     """Create *count* tests in various pipeline states."""
     if not techniques:
         logger.warning("No techniques available — skipping test seeding.")
@@ -267,7 +269,7 @@ def _seed_tests(db, users: list[User], techniques: list[Technique], count: int =
     return tests
 
 
-def _seed_evidences(db, tests: list[Test], users: list[User], count: int = 50) -> list[Evidence]:
+def _seed_evidences(db: Session, tests: list[Test], users: list[User], count: int = 50) -> list[Evidence]:
     """Create *count* dummy evidence records."""
     if not tests:
         return []
@@ -305,7 +307,7 @@ def _seed_evidences(db, tests: list[Test], users: list[User], count: int = 50) -
     return evidences
 
 
-def _seed_audit_logs(db, users: list[User], count: int = 20) -> None:
+def _seed_audit_logs(db: Session, users: list[User], count: int = 20) -> None:
     """Create *count* varied audit log entries."""
     for i in range(count):
         user = random.choice(users)
@@ -323,7 +325,7 @@ def _seed_audit_logs(db, users: list[User], count: int = 20) -> None:
     logger.info("Created %d demo audit logs.", count)
 
 
-def _seed_notifications(db, users: list[User], count: int = 30) -> None:
+def _seed_notifications(db: Session, users: list[User], count: int = 30) -> None:
     """Create *count* notifications spread across demo users."""
     for i in range(count):
         user = random.choice(users)
@@ -344,7 +346,7 @@ def _seed_notifications(db, users: list[User], count: int = 30) -> None:
     logger.info("Created %d demo notifications.", count)
 
 
-def _seed_templates(db, techniques: list[Technique], count: int = 10) -> None:
+def _seed_templates(db: Session, techniques: list[Technique], count: int = 10) -> None:
     """Create *count* manual demo templates."""
     if not techniques:
         return