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.

internal/config/config.go

@@ -10,6 +10,7 @@ import (
 // Config holds the control plane configuration.
 type Config struct {
 	DatabaseURL   string
+	RedisURL      string
 	ListenAddr    string
 	HostAgentAddr string
 	JWTSecret     string
@@ -28,6 +29,7 @@ func Load() Config {
 
 	cfg := Config{
 		DatabaseURL:   envOrDefault("DATABASE_URL", "postgres://wrenn:wrenn@localhost:5432/wrenn?sslmode=disable"),
+		RedisURL:      envOrDefault("REDIS_URL", "redis://localhost:6379/0"),
 		ListenAddr:    envOrDefault("CP_LISTEN_ADDR", ":8080"),
 		HostAgentAddr: envOrDefault("CP_HOST_AGENT_ADDR", "http://localhost:50051"),
 		JWTSecret:     os.Getenv("JWT_SECRET"),