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!

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/routers/techniques.py

@@ -45,7 +45,7 @@ def list_techniques(
     review_required: bool | None = Query(None, description="Filter by review flag"),
     repo: SATechniqueRepository = Depends(get_technique_repository),
     current_user: User = Depends(get_current_user),
-):
+) -> list:
     """Return a lightweight list of techniques, optionally filtered."""
     return repo.list_all(
         tactic=tactic,
@@ -64,7 +64,7 @@ def get_technique(
     mitre_id: str,
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> dict:
     """Return full details for a single technique, including its tests and D3FEND defenses."""
     return get_technique_detail(db, mitre_id)
 
@@ -84,7 +84,7 @@ def create_technique(
     db: Session = Depends(get_db),
     repo: SATechniqueRepository = Depends(get_technique_repository),
     current_user: User = Depends(require_role("admin")),
-):
+) -> TechniqueOut:
     """Create a new technique manually."""
     if repo.exists_by_mitre_id(payload.mitre_id):
         raise DuplicateEntityError("Technique", "mitre_id", payload.mitre_id)
@@ -124,7 +124,7 @@ def update_technique(
     db: Session = Depends(get_db),
     repo: SATechniqueRepository = Depends(get_technique_repository),
     current_user: User = Depends(require_role("admin")),
-):
+) -> TechniqueOut:
     """Update one or more fields of an existing technique."""
     entity = repo.find_by_mitre_id(mitre_id)
     if entity is None:
@@ -160,7 +160,7 @@ def review_technique(
     db: Session = Depends(get_db),
     repo: SATechniqueRepository = Depends(get_technique_repository),
     current_user: User = Depends(require_any_role("red_lead", "blue_lead")),
-):
+) -> TechniqueOut:
     """Mark a technique as reviewed.
 
     Sets ``review_required`` to *False* and records the current timestamp