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/osint.py

@@ -57,7 +57,7 @@ def list_osint_items(
     limit: int = Query(50, ge=1, le=200),
     db: Session = Depends(get_db),
     user: User = Depends(get_current_user),
-):
+) -> list:
     """List OSINT items with optional filters."""
     return service_list_osint_items(
         db,
@@ -73,7 +73,7 @@ def list_osint_items(
 def osint_summary(
     db: Session = Depends(get_db),
     user: User = Depends(get_current_user),
-):
+) -> dict:
     """Summary statistics for OSINT items."""
     return get_osint_summary(db)
 
@@ -83,7 +83,7 @@ def review_osint_item(
     item_id: UUID,
     db: Session = Depends(get_db),
     user: User = Depends(get_current_user),
-):
+) -> dict:
     """Mark an OSINT item as reviewed."""
     with UnitOfWork(db) as uow:
         item = mark_osint_reviewed(db, str(item_id))
@@ -101,7 +101,7 @@ def trigger_technique_enrichment(
     technique_id: UUID,
     db: Session = Depends(get_db),
     user: User = Depends(require_any_role("red_lead", "blue_lead")),
-):
+) -> dict:
     """Manually trigger OSINT enrichment for a single technique."""
     technique = get_technique_or_raise(db, technique_id)
     count = enrich_technique_with_cves(db, technique)
@@ -119,7 +119,7 @@ def get_technique_osint(
     reviewed: bool | None = Query(None),
     db: Session = Depends(get_db),
     user: User = Depends(get_current_user),
-):
+) -> list:
     """Get all OSINT items for a specific technique."""
     items = get_osint_items_for_technique(
         db,