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/database.py

@@ -1,5 +1,8 @@
+from collections.abc import Generator
+
 from sqlalchemy import create_engine
-from sqlalchemy.orm import declarative_base, sessionmaker
+from sqlalchemy.engine import Engine
+from sqlalchemy.orm import Session, declarative_base, sessionmaker
 
 Base = declarative_base()
 
@@ -10,7 +13,7 @@ _engine = None
 _SessionLocal = None
 
 
-def _get_engine():
+def _get_engine() -> Engine:
     global _engine
     if _engine is None:
         from app.config import settings
@@ -28,7 +31,7 @@ def _get_engine():
     return _engine
 
 
-def _get_session_factory():
+def _get_session_factory() -> sessionmaker:
     global _SessionLocal
     if _SessionLocal is None:
         _SessionLocal = sessionmaker(
@@ -41,10 +44,10 @@ class _LazySessionLocal:
     """Proxy so ``SessionLocal()`` keeps working as before but the real
     sessionmaker is only created on first call."""
 
-    def __call__(self, *args, **kwargs):
+    def __call__(self, *args: object, **kwargs: object) -> Session:
         return _get_session_factory()(*args, **kwargs)
 
-    def __getattr__(self, name):
+    def __getattr__(self, name: str) -> object:
         return getattr(_get_session_factory(), name)
 
 
@@ -53,14 +56,14 @@ SessionLocal = _LazySessionLocal()
 
 class _EngineProxy:
     """Thin proxy so ``from app.database import engine`` still works."""
-    def __getattr__(self, name):
+    def __getattr__(self, name: str) -> object:
         return getattr(_get_engine(), name)
 
 
 engine = _EngineProxy()  # type: ignore[assignment]
 
 
-def get_db():
+def get_db() -> Generator[Session, None, None]:
     db = SessionLocal()
     try:
         yield db