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

docker-compose.yml

@@ -55,6 +55,22 @@ services:
       retries: 5
     restart: unless-stopped
 
+  # ── Redis ──────────────────────────────────────────────────────────────────
+  redis:
+    image: redis:7-alpine
+    container_name: aegis-redis
+    command: redis-server --appendonly yes --maxmemory 256mb --maxmemory-policy allkeys-lru
+    ports:
+      - "6379:6379"
+    volumes:
+      - redis_data:/data
+    healthcheck:
+      test: ["CMD", "redis-cli", "ping"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+    restart: unless-stopped
+
   # ── FastAPI Backend ────────────────────────────────────────────────────────
   backend:
     build:
@@ -71,6 +87,8 @@ services:
       # Set it explicitly if you need persistent sessions across restarts.
       ALGORITHM: HS256
       ACCESS_TOKEN_EXPIRE_MINUTES: 60
+      # Redis
+      REDIS_URL: redis://redis:6379/0
       # MinIO
       MINIO_ENDPOINT: minio:9000
       MINIO_ACCESS_KEY: minioadmin
@@ -80,6 +98,8 @@ services:
     depends_on:
       postgres:
         condition: service_healthy
+      redis:
+        condition: service_healthy
       minio:
         condition: service_started
     volumes:
@@ -117,3 +137,5 @@ volumes:
     name: aegis_postgres_data
   minio_data:
     name: aegis_minio_data
+  redis_data:
+    name: aegis_redis_data