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/metrics.py

@@ -42,7 +42,7 @@ router = APIRouter(prefix="/metrics", tags=["metrics"])
 def coverage_summary(
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> CoverageSummary:
     """Return a global coverage summary across all techniques."""
     return get_coverage_summary(db)
 
@@ -56,7 +56,7 @@ def coverage_summary(
 def coverage_by_tactic(
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> list[TacticCoverage]:
     """Return coverage breakdown grouped by tactic."""
     return get_coverage_by_tactic(db)
 
@@ -70,7 +70,7 @@ def coverage_by_tactic(
 def test_pipeline(
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> TestPipelineCounts:
     """Return how many tests are in each pipeline state."""
     return get_test_pipeline_counts(db)
 
@@ -84,7 +84,7 @@ def test_pipeline(
 def team_activity(
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> list[TeamActivity]:
     """Return activity summary for Red and Blue teams."""
     return get_team_activity(db)
 
@@ -98,7 +98,7 @@ def team_activity(
 def validation_rate(
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> list[ValidationRate]:
     """Return approval and rejection rates for Red Lead and Blue Lead."""
     return get_validation_rate(db)
 
@@ -112,6 +112,6 @@ def validation_rate(
 def recent_tests(
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
-):
+) -> list[RecentTestItem]:
     """Return the 10 most recently created tests."""
     return get_recent_tests(db, limit=10)