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/routers/test_templates.py

@@ -78,7 +78,7 @@ def _list_templates_handler(
     limit: int = Query(50, ge=1, le=200),
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> list:
     """Return a paginated, filterable list of test templates."""
     return list_templates(
         db,
@@ -102,7 +102,7 @@ def _list_templates_handler(
 def template_stats(
     db: Session = Depends(get_db),
     current_user: User = Depends(require_any_role("red_lead", "blue_lead")),
-):
+) -> dict:
     """Return catalog statistics: active, by_source, by_platform."""
     return get_template_stats(db)
 
@@ -117,7 +117,7 @@ def bulk_activate_templates(
     activate: bool = Query(True, description="True to activate all, False to deactivate all"),
     db: Session = Depends(get_db),
     current_user: User = Depends(require_any_role("red_lead", "blue_lead")),
-):
+) -> dict:
     """Set all templates to active or inactive."""
     count = bulk_activate(db, activate=activate)
     with UnitOfWork(db) as uow:
@@ -148,7 +148,7 @@ def _templates_by_technique_handler(
     mitre_id: str,
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> list:
     """Return all active templates mapped to a specific MITRE technique."""
     return templates_by_technique(db, mitre_id)
 
@@ -163,7 +163,7 @@ def get_template(
     template_id: uuid.UUID,
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> TestTemplateOut:
     """Return full details for a single test template."""
     return get_template_or_raise(db, template_id)
 
@@ -182,7 +182,7 @@ def create_template(
     payload: TestTemplateCreate,
     db: Session = Depends(get_db),
     current_user: User = Depends(require_any_role("red_lead", "blue_lead")),
-):
+) -> TestTemplateOut:
     """Create a custom test template."""
     template = create_template_svc(db, **payload.model_dump())
     with UnitOfWork(db) as uow:
@@ -215,7 +215,7 @@ def update_template(
     payload: TestTemplateCreate,
     db: Session = Depends(get_db),
     current_user: User = Depends(require_any_role("red_lead", "blue_lead")),
-):
+) -> TestTemplateOut:
     """Update fields of an existing test template."""
     template = update_template_svc(db, template_id, **payload.model_dump(exclude_unset=True))
     with UnitOfWork(db) as uow:
@@ -243,7 +243,7 @@ def toggle_template_active(
     template_id: uuid.UUID,
     db: Session = Depends(get_db),
     current_user: User = Depends(require_any_role("red_lead", "blue_lead")),
-):
+) -> TestTemplateOut:
     """Toggle a template between active and inactive (is_active = not is_active)."""
     template = toggle_template_active_svc(db, template_id)
     with UnitOfWork(db) as uow:
@@ -271,7 +271,7 @@ def delete_template(
     template_id: uuid.UUID,
     db: Session = Depends(get_db),
     current_user: User = Depends(require_any_role("red_lead", "blue_lead")),
-):
+) -> dict:
     """Soft-delete a test template by setting ``is_active=False``."""
     template = get_template_or_raise(db, template_id)
     soft_delete_template(db, template_id)