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/professional_reports.py

@@ -29,7 +29,7 @@ def generate_purple_report(
     format: str = Query("pdf", pattern="^(pdf|docx|html)$"),
     db: Session = Depends(get_db),
     user: User = Depends(require_any_role("red_lead", "blue_lead", "viewer")),
-):
+) -> FileResponse:
     """Generate a Purple Team campaign assessment report."""
     filepath = report_generation_service.generate_purple_campaign_report(
         db, str(campaign_id), output_format=format,
@@ -48,7 +48,7 @@ def generate_coverage_report(
     format: str = Query("pdf", pattern="^(pdf|docx|html)$"),
     db: Session = Depends(get_db),
     user: User = Depends(require_any_role("red_lead", "blue_lead", "viewer")),
-):
+) -> FileResponse:
     """Generate an organization-wide MITRE ATT&CK coverage report."""
     filepath = report_generation_service.generate_coverage_report(
         db, output_format=format,
@@ -67,7 +67,7 @@ def generate_executive_report(
     format: str = Query("pdf", pattern="^(pdf|docx|html)$"),
     db: Session = Depends(get_db),
     user: User = Depends(require_any_role("red_lead", "blue_lead", "viewer")),
-):
+) -> FileResponse:
     """Generate an executive security summary report."""
     filepath = report_generation_service.generate_executive_summary(
         db, output_format=format,
@@ -86,7 +86,7 @@ def generate_quarterly_report(
     format: str = Query("pdf", pattern="^(pdf|docx|html)$"),
     db: Session = Depends(get_db),
     user: User = Depends(require_any_role("red_lead", "blue_lead", "viewer")),
-):
+) -> FileResponse:
     """Generate a quarterly security summary report."""
     filepath = report_generation_service.generate_quarterly_summary(
         db, output_format=format,
@@ -106,7 +106,7 @@ def generate_technique_report(
     format: str = Query("pdf", pattern="^(pdf|docx|html)$"),
     db: Session = Depends(get_db),
     user: User = Depends(get_current_user),
-):
+) -> FileResponse:
     """Generate a detailed report for one MITRE technique."""
     filepath = report_generation_service.generate_technique_detail_report(
         db, str(technique_id), output_format=format,