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/app/routers/auth.py

@@ -98,8 +98,9 @@ def logout(
 ):
     """Clear the authentication cookie and revoke the current token.
 
-    The token's ``jti`` is added to an in-memory blacklist so it cannot
+    The token's ``jti`` is added to the Redis blacklist so it cannot
     be reused even if the cookie has already been copied elsewhere.
+    The blacklist entry auto-expires when the token's ``exp`` is reached.
     """
     # Attempt to blacklist the token's jti
     token = aegis_token or request.headers.get("Authorization", "").removeprefix("Bearer ").strip()