feat: add admin console, Redis broker and chaos lab for training demo

.env.example

@@ -37,3 +37,21 @@ DATABASE_URL=postgres://postgres:postgres@db:5432/guestbook?sslmode=disable
 # DB_PASSWORD=postgres
 # DB_NAME=guestbook
 # DB_SSL_MODE=disable
+
+# === Scaling / live updates ========
+# Redis for cross-replica live updates and presence. Without it each replica
+# only pushes to its own clients. On Miabi, attach a managed Redis with the
+# "REDIS" env prefix and REDIS_DATABASE_URL is injected (also accepted).
+# REDIS_URL=redis://redis:6379
+
+# === Admin console =================
+# Enables /admin. Store as a secret. Generate with: openssl rand -hex 16
+# ADMIN_TOKEN=
+
+# CIDRs whose X-Forwarded-For is trusted for the signer IP shown in /admin.
+# Unset trusts the header as-is (fine behind the Miabi gateway).
+# TRUSTED_PROXIES=10.0.0.0/8
+
+# Expose /api/debug/* failure injection (crash, slow, 5xx, CPU, memory, logs).
+# Still requires admin auth. Demo environments only.
+# DEBUG_ENDPOINTS=false