feat(infra): add Redis service and client for Phase 0 [FASE-0.1]

Add Redis 7 to Docker Compose with healthcheck and persistence, separate logical DBs for blacklist and cache, singleton redis client helpers, and unit tests with fakeredis.

docker-compose.yml

@@ -69,7 +69,7 @@ services:
       interval: 5s
       timeout: 3s
       retries: 5
-    restart: unless-stopped
+    restart: always
 
   # ── FastAPI Backend ────────────────────────────────────────────────────────
   backend:
@@ -89,6 +89,8 @@ services:
       ACCESS_TOKEN_EXPIRE_MINUTES: 60
       # Redis
       REDIS_URL: redis://redis:6379/0
+      REDIS_TOKEN_BLACKLIST_DB: "1"
+      REDIS_CACHE_DB: "2"
       # MinIO
       MINIO_ENDPOINT: minio:9000
       MINIO_ACCESS_KEY: minioadmin