feat(phase-34): resolve blocking tech debt — Redis, domain exceptions, indexes, CI

Foundational changes required before any new feature work can begin.

- 0.1 Redis infrastructure: add redis:7-alpine to docker-compose dev and prod,
  REDIS_URL config, singleton client in app/infrastructure/redis_client.py
- 0.2 Token blacklist on Redis SEC-001: replace in-memory dict with Redis SETEX
  keyed by jti, auto-expiring TTL derived from token exp
- 0.3 Database indexes SR-006: Alembic migration b019 with 5 composite indexes
  for scoring, MTTD/MTTR, remediation, and notification queries
- 0.4 Domain exceptions TD-003: app/domain/exceptions.py with typed errors,
  error_handler middleware mapping them to HTTP, services decoupled from FastAPI
- 0.5 Fix silenced exceptions TD-007: replace 4 bare except-pass blocks in
  test_workflow_service with logger.warning with exc_info
- 0.6 CI pipeline TD-009: GitHub Actions workflow with Postgres and Redis
  service containers, ruff lint, pytest; ruff.toml for baseline config

backend/tests/test_campaigns_and_snapshots.py

@@ -142,7 +142,7 @@ class TestCampaigns:
 
     def test_circular_dependency_prevention(self, db, campaign_with_tests):
         """Intentar crear dependencia circular en campaign_tests falla."""
-        from fastapi import HTTPException
+        from app.domain.exceptions import InvalidOperationError
 
         campaign = campaign_with_tests["campaign"]
         cts = (
@@ -157,11 +157,11 @@ class TestCampaigns:
         db.commit()
 
         # Try to create B -> A (circular)
-        with pytest.raises(HTTPException) as exc_info:
+        with pytest.raises(InvalidOperationError) as exc_info:
             validate_no_circular_dependency(
                 db, campaign.id, cts[0].id, cts[1].id
             )
-        assert exc_info.value.status_code == 400
+        assert exc_info.value.code == "INVALID_OPERATION"
 
     def test_campaign_scheduling_next_run(self):
         """next_run_at se calcula correctamente para weekly/monthly/quarterly."""