Add admin users, BYOC teams, hosts schema, and Redis for host registration

Introduce three migrations: admin permissions (is_admin + permissions table),
BYOC team tracking, and multi-host support (hosts, host_tokens, host_tags).
Add Redis to dev infra and wire up client in control plane for ephemeral
host registration tokens. Add go-redis dependency.

.env.example

@@ -1,6 +1,9 @@
 # Database
 DATABASE_URL=postgres://wrenn:wrenn@localhost:5432/wrenn?sslmode=disable
 
+# Redis
+REDIS_URL=redis://localhost:6379/0
+
 # Control Plane
 CP_LISTEN_ADDR=:8000
 CP_HOST_AGENT_ADDR=localhost:50051